Selfishly looking at it, you're right, it's pointless. The purpose is to whittle down the defences so that stronger players can break through them (at all or more easily with higher kill count).
I'd like to point out that 10k Marauders is a small suicide wave (600k-1.5M off, depending on your upgrades/items/relics/prestige). It is a small sacrifice. You can train that in 18 days (550 per day).
In my BH, we require 5+ million (3M for small missions). Each wave can have 3 players, so 3*5M = 15M. That does do some damage and wins some points. A 150 members BH can have 40+ of those waves, which is 40*15M = 600M hits (doesn't work exactly like 600M because they don't hit at once, but they still hurt defenders). Then, when the big guns hit in the end, the defences are significantly weakened, so they sustain lower losses (for a player who sends 200+ million at once, revival will be expensive and any savings are welcome) while also killing more of the def than without suicides.
So, it boils down to this: do you play only for yourself or are you willing to do suboptimal hits (from your perspective) in order to help your BH. I'm not judging here, but I do advise you pick a BH that doesn't expect that kind of participation if you don't want to do it.