Same reason why the Linux desktop often suffers on the UX/UX front: people naturally drawn to these projects tend to lean heavily technical, and highly technical circles have a bad habit of driving out less technical contributors through devaluation of their work and lack of agency within the project among other issues.
That sort of work also tends to be less well-compensated than that of SWEs which makes it more important to be paid for work (which most FOSS project cannot do).
That sort of work also tends to be less well-compensated than that of SWEs which makes it more important to be paid for work (which most FOSS project cannot do).