The thing is, if someone happens to be a good landlord and take their responsibilities seriously, everyone probably benefits from them having more rental properties as they become skilled and proficient in providing a good service.
There's a lot of people who have maybe accidentally become landlords and while I am sure many of them are good, it's a lot harder work for them to ensure they do a very good job, up to date with all regulations, knowledgeable about good electricians, plumbers, legislation etc. It's proportionately a lot more work for them per property I think.
They are also more likely to become vulnerable to financial pressures themselves, and be unable to accommodate short-term financial difficulties tenants experience with rent payments, and suddenly want to sell, rather than being able to provide long-term security for tenants.
I think it was a vague Labour manifesto issue at some point that all private rental properties be forcibly sold and councils took over. But that would flood the market with properties suddenly and all house prices would go down (which would at least be good for first time buyers.) And then the councils would have to take over and be more exposed to risk in terms of house price crashes, defaulting rent payments, whereas what you have at the moment is hundreds of thousands or millions of landlords who are taking that risk on themselves.
I definitely think there should be more regulation and quick complaints, appeals processes to resolve issues quickly. In Scotland there is a system to take away the registration of landlords who are failing their tenants so that they can not rent out properties when they no longer have this...but it is a slow process.