I think the big reason they're so huge is they make it easy to onboard alllll your data, and incentivise you financially to stick with all their custom tooling

I think the big reason they're so huge is they make it easy to onboard alllll your data, and incentivise you financially to stick with all their custom tooling and instrumentation. So the "quick wins" have a long tail of financial scaling. As your own scale grows, your DD costs grow. And so you do a few things that may entrench you further to drop your costs and the sunk cost fallacy helps corner you. You need your dashboards and alerts now that you're bigger, so you aren't thrilled about the prospect of rebuilding from scratch. Anyway, I know this because I've been there at a former employer. We started off (and mostly stayed) otel at the base layers, but more and more had to move to proprietary DD collectors/agents for off-the-shelf system metrics (db, cloud, VMs, k8s, etc), because otherwise they were custom metrics and very very expensive. So they're very very sticky. And the market loves a sticky + expensive vendor.