The Hand History viewer (HHV) has been changed a couple of times since HM2 was released, and those changes were made based on users opinions. But no redesign or huge changes were made, just small things here and there. The all idea behind the design of HM2 HHV it's still present today: grey background with lighter grey fonts, that don't popup easily, line by line plays (corrected bellow), small cards, etc.
Basically, i assume, from outside, they wanted to move completely from the HH1 design that was very successful. Even today you'll see people making suggestion that mimic the old HM1 HHV, or PT4, which is a copy of HM1. All those suggestion, that have any resemblance from the old HM1 HHV were NOT implemented. I'm sure there is a reason for this.
I have used HM2 since it was in beta phase, and TODAY i can't get used to the HHV. I can use HM1 or PT4 HHV just fine, there must be a reason for this. It toke me a couple of months to get used to HM2, from years and years using HM1, but i finally stop opening HM1. So, yeh, this isn't just me being an old guy that doesn't like changes, there's definitely something not quite right with the HHV design.
Anyway, dissection, they welcome suggestions, and if there are a lot of people behind those suggestion they make it happen. Just takes time, which usually frustrate people and make them write stupid posts like... i sometimes do. Personally, and to be fair, i have made a hand full of suggestion/critics/etc over the years and they were implemented/corrected.
Edit:
My memory is not what it used to be. Here is one of the first version of HM2 vs HM1 HVV:
HM1 had line by line plays, and HM2 first HHV version had one line plays. I could almost swear that was the other way around.
Anyway, i was wrong about that but i'm not going to edit it. It is what it is.
Edit 2:
Then, this was the next improved version: