Here's a thought I just had: backwards compatibility will keep old customers happy while breaking changes make a certain percentage of them quit your platform or perhaps just complain loudly on Internet forums. But if you keep your product modern and flexible, free of cruft, then you're able to pivot quickly when new technology, new markets, and new products demand it, and address the ever growing market. New customers and developers are being born every day or in the developing world coming into the market. These will outstrip any losses you have from grumbling ex-customers. Being able to address their needs is probably more profitable.

Sidenote - it's funny that Microsoft is so stable for their customer base while just constantly churning their frameworks and APIs. I worked in an MS shop, and boy, it seemed like they were introducing a new GUI or Web framework every six months, while of course slowing down or deprecating the older ones.