Zoning regulations to prevent the supply from meeting the demand. Since the 1950s cities made zoning regulations that only allow two kinds of properties to be built, detacted single family houses in the suburbs and high rise condo buildings in the downtown core and not other properties such as smaller apartment buildings, multiplex housing, townhouses, etc. Any building that's not a detached single family house or a high rise condo building is referred to as "missing middle housing". Rent is getting more and more expensive every year in cities because of this but there is one city where that's not the case, Minneapolis and that's because they got rid of the strict zoning laws, some other cities are getting rid of strict zoning laws too such as Tacoma, Washington and Toronto, Ontario, Canada. You are right, landlords are necessarily the main problem but a symptom of the problem but there are also landlords who badly screw over the tennants, I can tell you this from first hand experience. I've had multiple landlords screw me over and try to evict me at whim even though I wasn't in rent arrears, one time a landlord and his real estate agent representing him tried to get 3 months of rent out of me and then refused to rent to me and rented to someone else even though I signed the contract they sent me that was also signed by the landlord and real estate agent, they committed breach of contract on me.
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