Would you like to force everything to be SSL? Another plugin. Do you want a contact form? Another plugin. Do you want to disable the bizarre update messages from ignite woo that won't go away? Another plugin. Oh, you want some slider-carousel thing on some page? Another plugin. Caching? Another plugin. Image optimization? Another plugin. Some sort of 'maintenance mode' to deal with taking down the site for upgrades? Another plugin. Social sharing buttons? Another plugin.
I could keep going, but perhaps you get the picture. And the argument could be made that 90% of these are not needed, and there's other ways to deal with the requirements. In my most recent excursion, I'd taken over a project from someone else, and this was it. Any changes to anything would require investigation, custom code, and still require some sort of UI to manage things, all of which cost time and money, which were in short supply, so this particular project kept going with dozens of plugins.
You want to do an upgrade to WP core? You've got 30+ plugins to test. Or... just click 'update' and hope for the best. Or test each plugin and upgrade process on a separate server. Again, back to relatively large amounts of time and money expended just to keep up with wp core to avoid inevitable hacking attempts.
I have another multisite install I was brought in on over the summer, with 165 plugins. It's just another version of 'crappy legacy software and undocumented crap with no documentation' which we've all seen, but it is also quantified by "number of wp plugins". No, not every site is using all 165. But there were/are > 40 sites, with various groups using various combinations - there's 0 good reasons for all of these to have been combined (over several years) in to one massive multisite mess, but it was, and it's taken many people far too long to unravel some of the mess to extricate some sites.
Yes, some of this is just a 'bad code is bad code' rant, but given the mindshare that WP owns, it would seem to be incumbent on them to raise the bar with respect to tools for plugin management (as just one example), give developers better starting code and samples and guidance for what's acceptable and what's not. A paid certification program which would vet code for 'best practices' would be something I think would help improve the landscape in short order (and no doubt has been considered by some over the years).