That's a great question and we have great answers from actual clients - the repeating pattern goes as follows:

"We invested three years building this app, it's a booming success, but their user-based pricing is killing us"

"We can't run complex queries"

"It's too slow"

"We feel our data is stuck there"

"I want to own my code and my application"

"Why do I need to use APEX where we use Java and JS everywhere else in the company"