I know. However if you have lots of devices it will be quite some pain in the ass to unpair them from one hub, add them to another and recreate all the rules.
And of course there's always the possibility that the new hub doesn't support the same protocols then the old one. Or maybe it does, but there are some incompatibilities within device support and some of your devices won't work anymore.
As opposed to Control4 and Crestron systems that require $$$$ and a tech to come out every time you want to make a change, no thank you.
Sure, if SmartThings goes the way of Revolv and bites the dust I'll have to buy a new IOT gateway de jour and set my stuff back up, but that's maybe an hour or two of work if you know how your devices work and can read a manual.
And of course there's always the possibility that the new hub doesn't support the same protocols then the old one. Or maybe it does, but there are some incompatibilities within device support and some of your devices won't work anymore.