I don't understand it and never will but you don't spoil my day out so crack on doing what you want to do fella ;-)
As you say people can do whatever they want - but it was refreshing to see more people stay until the end against Shakhtar.
I have a ST in the family stand and Champions League is a very different demographic to league matches - there was a far better vibe in there than usual because I think a lot of people were there as a one-off match and wanted to enjoy every minute.
Whatever the reasons for leaving early it's undeniable that having more people there at the end of the match is favourable to playing in front of a half empty stadium. Hopefully some of the people that go as a one-off enjoy it and become regular match going fans.