Why is it a problem for Malzahar to force low agency but not Blitz?

So the whole thing with Riots Malzahar changes were to address the "Low agency" play of the champion.

Fair enough, as a Malzahar main I cant say im actually unhappy with the choices Riot is going with. But it did raise a question for me, There are a lot of champions that have that exact same unrelenting pressure, and there isnt much an opponent can do about it.

Blitzcrank immediately springs to mind. Not that Blitz is all that hard to counter, but he forces a style of play out of a bot lane. Always staying behind minions, never going near the enemy tower, terrified running if he trys to flank. Much like Malz, a Blitz doesnt guarantee a win. (although Malz has always had a high win rate) But he does force the same kind of play out of opponents.

Veigar is also like this, with 40 cdr his e and r are basically always up and you simply cant go near him or you will be gone.

I guess at the end of the day, I'm simply wondering if these champions will eventually be changed as well.