The biggest loss I've seen in buying software (and I've been in large companies that have gone both ways) is agility.
If you're using a vendor solution w/o source rights, and you need a new feature to pursue a new opportunity... you can't.
Best case, the vendor is persuaded they can make money from it, develops it, and offers it to all their other customers. Middle case, they charge you an arm and a leg for custom functionality (more than it actually costs to develop), and now you're off the main tree. Worst case, they ignore you or refuse.
So the primary benefit to owning your own software development is the ability to pivot to new opportunities.
E.g. You think AWS would exist if Amazon had outsourced their server management software?
If you're using a vendor solution w/o source rights, and you need a new feature to pursue a new opportunity... you can't.
Best case, the vendor is persuaded they can make money from it, develops it, and offers it to all their other customers. Middle case, they charge you an arm and a leg for custom functionality (more than it actually costs to develop), and now you're off the main tree. Worst case, they ignore you or refuse.
So the primary benefit to owning your own software development is the ability to pivot to new opportunities.
E.g. You think AWS would exist if Amazon had outsourced their server management software?