I was there years ago but the main reason was support. I worked on the Enterprise/Custom (largest clients, minimum 5 figure MRR/month) team and the phones were staffed by actual System Engineers/Admins 24/7. It might be one guy overnight but if you were the CTO of $bigname and needed something done, from SQL restores, migrations, etc all you had to do was dial in. No phone tag, no wait, no voicemails.

We were very expensive but the companies must have saved money in hiring their own Engineers as were always growing.

AWS/GCP/Azure have made doing a lot of what we used to do incredibly more accessible to more people.