> Sure, but it's more than frustrating to go to a lawyer for a service you are supposed to just get [...]
Of course. In a healthy market (low transactions costs and sufficient number of participants leads to sufficient volume and price discovery, and thus competition, which eliminates economic rent seekers) you simply stop using the bad provider and switch to a good provider. Of course people hate moving even more than contracting an attorney.
And that's why advanced economies need consumer protection bureaus/agencies to counteract these inefficiencies. So they should bring the lawsuits to weed out the bad providers and incentivize keeping the terms of the contracts.
Unfortunately in the US these agencies are either non-existent or pretty weak, and their place was taken by class action lawsuits brought by opportunistic law firms.
> modernizations justify higher rents.
Well, a rental unit is like a field in a farm. Or maybe compare it to a greenhouse. If you replace the insulation on the greenhouse to something better now you can cultivate more/better plants, which means you make more money.
Investments (by definition) increase the capital value of the asset. More capital produces more output, so it can be exchanged for more money. For a housing unit the output is hedonistic value (aesthetic value, comfort value, better soundproofing, better plumbing, adding AC).
> Which is just nuts because why would a one-time investment justify a basically indefinitely going increased rent...
... it permanently increases the buying price of the unit. Just like with a house. If you renovate it you can sell it for more. If it's empty you can rent it out for more (in perpetuity).
The simple fact that there's a tenant doesn't change this.
Of course one must also consider amortization, but almost all rental agreements mandate that the owner actively maintain the unit, so its effect should be net zero, but if the market price of maintenance increases (because raw materials, plumbers, painters, etc. become more expensive) then it's not unreasonable for the rent to increase too. (And since the cost disease is especially affecting things manufactured/built/provided locally ... housing is getting a lot pricier. [0])
Also there's inflation. Which just by itself makes nominal rent increases a necessity.
[0] See https://phenomenalworld.org/analysis/the-class-politics-of-t... and http://web.archive.org/web/20191015142434/http://rationallys... ( https://www.stitcher.com/show/rationally-speaking/episode/ra... )