I don’t have a problem with the Files sidebar.
There is no reply other than the one @didrocks gave you, he basically gets the final say, we’re not on the desktop team, we don’t get to make these decisions. Note that you can join the desktop team and make decisions like this in the future, if you satisfy the requirements (which include experience, so you’ll need to contribute to Ubuntu first, we’re a meritocracy ( /dictatorship, due to the nature of the self-appointed benevolent dictator for life! ) not a democracy): https://wiki.ubuntu.com/DesktopTeam/Developers
Sometimes they ask for our opinion and consider the different opinions and use them to inform their judgments, but the final say is entirely up to them. There’s nothing than we can do other than accept the decision and meet the objections so that this doesn’t happen again next time and helping as many as possible to get onto the Communitheme (i.e. helping to make the snap, promoting the snap, developing the theme, holding the desktop team to account on their promise to get it in 18.10 early in the cycle (remember they never promised that it would be default in 18.04, it was always only a possibility)).