While there's sometimes maintainer-prima-donna egos the contend with there's also this:
Any patch sent in also needs to be maintained into the future, and most of the time it's the maintainers that need to do that, not the people contributing the patch. Therefore any feature-patches (as opposed to simple bugfixes) are quite often refused, even if they add useful functionality, because the maintainers conclude they will not be able to maintain the functionality into the future (because no one on the maintaining team has experience in a certain field, for example).
The quality bar for a 'drive by patch' which is contributed without the promise of future support is ridiculously high and it has to be. Other peoples' code is always harder to maintain than your own so it has to make up for that in quality.
Any patch sent in also needs to be maintained into the future, and most of the time it's the maintainers that need to do that, not the people contributing the patch. Therefore any feature-patches (as opposed to simple bugfixes) are quite often refused, even if they add useful functionality, because the maintainers conclude they will not be able to maintain the functionality into the future (because no one on the maintaining team has experience in a certain field, for example).
The quality bar for a 'drive by patch' which is contributed without the promise of future support is ridiculously high and it has to be. Other peoples' code is always harder to maintain than your own so it has to make up for that in quality.