It seems pretty obvious to me:
1) mega-threads are desirable to most people, buyers and sellers
2) a system that encourages and rewards mega-threads is desirable to most people as the result of #1. A system that merely allows mega-threads but makes them disadvantaged will force out mega-threads, which is undesirable to most people, which makes the system undesirable to most people.
The mods has every right to change the system to what is desirable to them, rather than...