Once at L5 it's okay to just stay there and do good work, the pay is still really good and you're not expected to go beyond that unless you want to (and you're capable of it).
The main issue I've heard is that to go from L3 -> L5 there are incentives around 'impact' and launching products (or leaving for another company/startup and getting hired back).
This means people are incentivized to ship something to get promo, but working on an already shipped thing is bad for career progress.
An oversimplification, but seen through this lens Google's many chat apps make sense.