You're not considering opportunity costs and buyers vs. users.

If your senior developers can slap together something better than an expensive SAAS offering you want them directing that energy at your core products/services rather than supporting tools.

And the people deciding to buy the expensive SAAS tools are often not the people using them, and typically don't care too much about how crappy the tool may or may not be for doing the job it's advertising as doing.

And it's never just the slapping together. it's the ktlo: a perpetual tax on your eng team for every thing they own.