Makes no sense, Holidays is supposed to be fun and enjoyable, not a stupid obstacle. Let people use the weapons that they goddamn want to use. It is bad enough that the troops themselves is restricted.
devs invented holiday events for people who don’t like GW
The holiday is making you by stuff for others enjoyment (devs).
Personally I think you got the question backwards: why are Hero weapons often exempt from troop requirements in other game modes (notably Delves) ?
I bet that if the required color was Yellow then you wouldn’t wait two seconds to put a Bard Hero on the team…
Because there is a gem shop in the event, same as all others?
Restricting weapons/troops may cause a lot of lower level players to spend more gems when they lose battles. This is how the ‘economy’ works