"Not Invented Here" is a real thing, and smart people do fall into it, but I'm reminded of a quote from Casey Muratori: "Those who do write their own code end up customers for those who do."
Pretty sure that should be "Those who don't write their own code end up customers for those who do." ?
And so what? There's nothing wrong with being a customer of someone else's code if they're good at what they do and what they do isn't what you're interested in doing.
It depends on what you want to get out of the process. If you're doing it for fun, write whatever you want. If your goal is the best possible product in a reasonable time frame, you make tradeoffs. If your goal is to make money, you make even more tradeoffs.