Why don't terrorists target only other terrorists?

That would be like a sniper targeting only other snipers.
They don't care WHOM they shoot. They're pissed off at the world, and are taking it out on anyone at hand.

The point of terrorism is to scare the general population into thinking that something bad can happen to anyone at any time. If the point was to take your gun and us humans for target practice, they could just shoot each other. That isn't the idea - you're angry at the world so the world has to know.

In inner cities you do have cases of criminals shooting other criminals and we don't hear about it.

That won't be a publicity stunt which is why they don't

With Islamic terrorist, their actions fuel islamicphobia, so countries like the US would show hatred to the Islamic people. If Islamic countries are being attacked by military strikes killing innocent people, they begin to hate those who lead the military strikes, and if those Islamic people are told "come join us, we're getting back at the people who attacked us" and that's a terrorist organization, the terrorists gain power. Terrorists want people to hate them

thats not how terrorism works...

That is the true Riddle of the Sphinx.

They do. Called government.

Why don't suicide bombers or murder-suicide perpetrators just skip right to the suicide?

They don't know who it is. This is kind of what civilized countries are trying to do, but you see it's not very effective so they often turn to bombing.