The wall of getting buy in for switching your company over to a new SCM is much higher if you need to move everything over to a new system and switch over all of your developers onto new software at the same time. And if things don't work out you have to do the same expensive process in reverse. On the other hand if you have git compatibility you can start with a small group of developers being able to try out the tool first and see if it is actually beneficial and work your way spreading it through the company. If it turns out the new thing isn't good it is trivial to go back to your old tools since you did not have to do expensive migrations.