They present their own issues such as cost and guest experience. The monorail is an aging system that Disney is unlikely to put as much effort into for the future. They didn't purchase new trains when they had the opportunity and the literal structural beams have shown wear and tear over the years with lack of feasibility in overhauling that. When the Skyliner was announced and as it opened there was a main thread for it and the amount of people reaming it for multiple reasons was extremely high. For one it can present issues for those with heights, for two it can abruptly (though I don't think is too common) shut down mid-ride and three it isn't good in inclement weather which pushes buses out to be used for that
Which mostly leaves more buses comment to which I agree with but I also know it's been hard to get bus drivers and costs. Disney chose not to have parking lot trams for way too long like stupidly long and also went back on their own public announcement of when those trams would be at each of the parks. It was largely understood to be a budgetary decision. I don't have much faith they would add more buses even if they could but I do agree that's a pretty simple solution.
As far as the driving comment while I understand the necessary snark with WDW they really haven't made it possible to do that for many of the resorts, the parks yes you can easily drive but the resorts especially the Deluxe ones parking there if you're not a hotel guest of that particular resort is very much an issue, Disney essentially forces you to take their own transportation these days to which may be a bus for the resorts not connected by Skyliner or by monorail and sometimes a bus is necessary if there is no Skyliner running or an issue with the monorails.