This "everything sucks (from my myopic viewpont)" thing is like a bizarre form of learned helplessness. And I say that as someone who complains a lot about the quality of tools and libraries. Only about 10% of the time do I think that means we should write our own. 40% we should pick a different tool, and half the time we should try to convince the author to fix the worst aspects (when the problem is deeper than a PR can address).
Code you wrote is easier to understand for you. Of course you're going to be more productive with your code but what about everybody else? Are you making any compromises for the comprehension of others? Do you remember nothing about middle- and high-school coaches complaining about 'ball hogs'?
The optimists think all of their code is amazing and bug free and hence cheap. But it costs everyone else time, respect (either for you, or themselves), but perhaps most importantly, resume material and independent support options. You are hijacking the project to fluff your own ego.
For me, the worst quartile of my jobs have been NIH that turned into codependent bullshit drama, and it causes a pretty intense histamine reaction (as is evidenced in my phrasing in this comment) for me with people who are not self-aware enough to allow at least the possibility that maybe 50 people who have been thinking hard about a problem for five years are better equipped to solve it than you can in a week of bravado, followed by months or years of dodging responsibility for the problems you created by substituting your judgement for the rest of the team and the entire Internet. Just get over yourself and be a team player for once in your miserable narcissistic life.
Certainly, though, it's disastrous to assume that some existing library/product/whatever is going to be superior to home-grown, just because a lot of people use it, there's a big company behind it, or etc. That piece of software was written to cover a certain area of design and business space, and that may not intersect very well with the design and business space you need covered.
For myself, I do start with the hope that I'll be able to avoid writing some big chunk of code (by using some existing piece of software). But I'm very wary, as external software comes with costs, even if it's "free".