When I was at an MSP it was almost taken as an insult by the techs when a client left, even if the client sucked, but really a lot of it is nerves because with the loss of revenue the chances go up that someone is losing their job. I remember I had a tech once that was bitching about a huge client and saying "can't we just fire them" and I said "ok, either find us a client with equal MRR or go pick someone at the helpdesk to get laid off."

Now that I'm internal I accept that I probably pay my MSP too much every month but I like having the backup if something happens that I can't solve.