That provide liquidity, open or manage channels for you, watch your channel so you don't lose your money or even hold your keys (as is the case with some popular wallets people recommend).
And the network itself centralizes around large hubs (otherwise route finding doesn't scale).
The repeated comments about "routing not scaling" are sort of weird, there's no real technical hurdle to overcome. Approximations of route finding are really all that's necessary, there's no strong centralizing force to be found there.
Uh, this kind of route finding is still an open problem, and there's not even an idea of how to address it.
Approximations don't scale, as routes will start failing more and more as the network grows(due to liquidity issues). Therefore routes will go through well-connected and well-funded nodes, which is the centralizing force you're looking for.
And the network itself centralizes around large hubs (otherwise route finding doesn't scale).