I think they have gone for the photos they have done in their tributes because they were happier, simpler times, and a lot of them were taken before Matt's addiction to pills and alcohol became so well-known amongst them all. Old school photos right back to when they all first met.
Whenever my best friend passed away, we all used old photos of us growing up not because we weren't close in the later stages of life, but more so because the earlier days were the oldest memories and certain photos just had so much meaning behind them.
I've currently just finished season 6 and am on to season 7 - you can see the difference in MP in the first episode of season 7 to the last one in season 6 - just shows what an unreal actor he was, he must have felt horrendous filming some of those scenes but to still show up - unreal

I know before when I went to work with a stinking hangover I felt like total
tit, got no work done, etc and that was just for an office job so I can't even imagine how he must have felt.