I like a kickback as much as anyone. But, kickbacks don't always work all the time, and sometimes you get wonky results out of them even when they do work.
One time I had a ball drain to the kickback, the kickback fired it back up it hit a post or something directly and went straight back down to the kickback again... Now, the time was still running so it got kicked out again, and it then hit the same spot and went straight back down. Only this time no more grace period.
I've also had the kickback fail to register and be unreliable. And that is frustrating when you have a pin and you can't rely on it.

I think its okay to try something new. As again we don't want every game to have a kickback. Just like I would say all these outlane ball saves will get old once every game starts to use them. But, remember the wire gates that some games had that would bring it back to the shooter lane. Those were fairly popular. I think styles evolve and change. And no doubt they will change again. I do think a few games in the future will have them, but yes mostly going forward it appears that trend is mostly abandoned.

As for pops. I disagree with you mostly, but I think you have merit to your argument, that they should be utilized more.
Iron Maiden you need to hit pops to get cyborg multiball(and also potentially an extra ball) and once in cyborg mb you need to hit them once to qualify for the jackpot shot.

Theater of Magic you need to hit the pops in the straight jacket escape to complete the mode.

Attack from Mars and MM you need to hit pops to get super pops... Granted that's just more points... But, who doesn't like points.
Monster Bash you need to hit the pops to dig out the mummy and qualify for that mode. You need the mummy mode to qualify for Monster bash wizard mode and of course monster of rock wizard mode.

I think Jurassic Park has a mode electric fence where you want to hit the pops to climb faster to get off the fence... I could be mistaken...

But, as a whole. I agree with what you say. It be nice if they had a little more focus around them. But, also as one poster mentioned above. The older games its useful to get them to score the rollovers. Which in some games can lead to big points.