First off - years ago there were not 5 flagship phones released from different manufacturers almost simultaneously.
Second - there was not as tight security on these devices making it more and more work for the developers
Third - Threads like this do not help development in any way. There is XDA-University and lots of threads that will help you modify your own device and possibly to create a ROM and start developing yourself.
XDA is a development site made by developers for developers, not a place where you get tons of free stuff to make your phone cool and whine about it when there is not enough free stuff made at great cost to developers personal and family time.
XDA Developers was founded by developers, for developers. It is now a valuable resource for people who want to make the most of their mobile devices, from customizing the look and feel to adding new functionality. Are you a developer?