Domestic terrorism, why arent we as a nation more concerned about the battle at home than the one that might come from abroad?

Because the vast majority of people don't believe that anything will ever happen to them.

Well, I think...Nah, on second thought ya'll have fun with that.

First of all, those things you mentioned are not terrorism. The one thing they all have in common is the shooter suffered mental health issues. And, in my opinion, there is much focus on these but the problem is, the focus is on the wrong aspect. One group of people looks at these and says "we have a mental health care problem in this country" while another group says "we need to ban guns". Well, in order to keep things simple, the first group is correct, though they have no answers beyond that. The problem is, no one has answers beyond that. The mental health care in this country is severely lacking in all aspects; diagnosis, definition, treatment, etc. It seems we send these people to get help, the help throws drugs at them and ships them back out to society as everything should be okay now. So I think you are mistaken when you say there is no focus on those issues.
When it does come to terrorism, the problem there lies in the fact that we live a world where people want to force political correctness down our throats, much to our detriment. When you have a president, agency heads, and other politicians who are afraid, or simply reluctant to call something terrorism because you don't want to offend this group or that, then we have a problem; but the application of that restraint is very selective.
The fact is, terrorists are here and they want to kill you. Some of these terrorist are domestic and some are international. Why sit here and say we should focus on one and not the other; Timothy McVeigh and the 9/11 attacks, what's the difference, really? They both killed a bunch of innocent on US soil. Beyond the other details (white vs Muslim, anti-government vs jihadist), what really is the difference? There is none. As I said, both attacks killed a bunch of people, both attacks occurred on US soil. Anyone could be a terrorist.
There is one area here I believe there is zero focus and, in my opinion, is potentially a bigger threat than the terrorists and the psycho shooters, that would be gangs. According to the FBI, there 1.5 million gang members in the US. Gangs account for up to 80% of crime in the US. Some of these gangs have strong ties to violent drug cartels (MS-13) and are equally brutal. Sure, you don't hear about gangland mass shootings, 1) because they don't get media attention 2) the victim is usually another gang member, 3)because it usually isn't a mass shooting. However, you can have 4 dead in a mass shooting and it's national news with loud calls for gun control, yet you can 8 people killed in a week from gangs and not a single word is said. Sure, the gangs mostly target each other, but they have targeted innocents, they target the police, and innocent citizens do get killed "accidentally" by gangs, What is to stop them from hitting innocent citizens on a regular basis when the "timing is right"?
You have asked a big question here and one without a simple or short answer The answer I have for you is "focus is lacking due to political agendas and ideologies, political correctness, and on the issue of mental health, there is no quick and easy solution so they run away from it and focus on guns and the only groups that can be targeted in a politically correct environment; the white right-wing Christians.

Everything you mentioned is not terrorism.
It's just crazy people.
A guy screams alah ice bar and then attacks someone/people that's a terrorist.
Domestic terrorism is instilling fear for a larger goal not attacking for the attack.

Rest assured there are many organizations on conus that are on patrol and watching.

Patriot Gaurd, OathKeepers, III%ers are just to name a few.

They are in the shadows.

Watching over funerals, fairing recruiting stations and watching the back of officers pumping gas or eating lunch.

They Are Everywhere.

You may have skipped classes the day they explained the "Fly Paper" theory. To be fair, your teachers may have omitted any mention of it. The concept is to engage the enemy elsewhere so they don't have to come looking here for us. It seems to have worked in the main thus far. (Let's hope it continues to work)

Ah, but you're not talking about terrorism, are you. You're talking about crime. That's a whole other subject that isn't taught to well these days. I almost hate to touch that one in 25 words or less, but here goes...

Crime rates vary in inverse proportion to enforcement. Inasmuch as enforcement is a local issue, crime rates vary greatly from place to place. For example, in America's major metropolitan areas where political correctness has hamstrung law enforcement, crime is rampant. In middle-America, where the rule of law is taught in homes, schools, and places of worship, and law enforcement is respected, civilians help them in the execution of their duties, crime is almost non-existent. Hate crimes also are rarer in these areas (which leads to another interesting discussion).

There you have it. Now, everybody on "3", you may jump all over me for this...1 - 2 - 3