More than anything, in my opinion, the pushing stuff one is seeing in the latest "big" shihan out of Japan seems to be related to the fact that it is more often than not staying clear of training environments that include 250 lbs aikidoka/uke.
Certainly, that's a factor, to say the least. On the other hand, the last few decades there have been many big westerners practicing at Hombu Dojo, so they have their share of big uke to deal with.
So, when it still gets to pushing and pulling, I believe it has a lot to do with the traditional authoritarian system prevailing at Hombu. A teacher is not to be questioned, his (yes, unfortunately it's still an exclusively male thing there) techniques not to be tested. So, they see the aikido world from inside an ivory tower, developing their techniques accordingly.
Of course, there are exceptions to this rule.