Is it worth the major part of a full time worker's income to have somebody take care of those things in the rare occasion they happen? Most normal people can easily fix their plumbing issues, a leaky roof, termites and such in a couple of days with a few hundreds of dollars in budget.

Landlords generally spend much less than 5% of their yearly rent income on maintenance. If they actually do something to improve an apartment, that is just an investment in their own real estate, that they own 100% even after having other people pay for it several times over during decades.

Edit: Or look at it this way: Would you hire and pay somebody a good salary for working maybe 5 or 10 days per year for you?