L.W admins are not profiting, they work for very little money, as i understand.

This is every instance admin though. They don't get a pass because they have a shitload of users. If anything the responsibility is even greater as one of the "flagship" instances. If they are unable to handle it then something needs to change.

They have troubles with the site and have been considering to drop it a few months ago.

I'm not really concerned with what the "official" excuses are as I find L.W staff to be untrustworthy. I haven't seen them talk about shutting L.W down but that sounds like a scare tactic to me. My personal opinion is that the fediverse doesn't need large instances in the first place though so I am obviously biased here.

My guess is that the protocol is heavy and since they have the largest instance there are bottlenecks.

Lemmy is a giant database that throws tantrums the more you add to it. As L.W is huge in terms of users and communities, I'm sure the demands on their hardware are very real. That doesn't change the fact that it isn't working correctly and sweeping genuine/good faith questions under the rug serves no purpose besides deception and ego protection.