Well there is the right to assemble, but as for why to bother the states do get some local political help from the coynventions.
It motivates the core of the party, kind of a emotional rally to help them put forth the tremendous grass roots effort to get the parties' candidates elected.
There doesn't seem to be much point to conventions anymore. The platform has been written and the candidates selected.Why bother?
Because the elites in politics like free beer. They like free wine. They like any kind of free party (and as delegates, they get all this stuff free). I agree with you that conventions are wasteful and useless in many regards... they really do fire up partisans, but few else. You have to think there'd be a better way to fire up the base than to have a huge convention that's boring to watch for most people who aren't there. But as long as elites keep putting their free wine and their status/ego-trips above the people they serve, you're going to have conventions. Sad fact. Even sadder, I know several people who were seriously talking about going to the Democratic convention and sneaking into parties with the delegates they knew, etc. Once again, it was just because they wanted to attend a big drunken party. I think that's incredibly shallow and that it misses what conventions should actually be about if they actually mattered at all, but that's just me.ZAP