I see.

The core of being a landlord is rent-seeking, or in other words monetising a superior economic position to extract a payment from those who do not have such a superior economic position.

You wouldn't be able to rent that room if other people had a choice to just easilly buy a small dwelling in that area for as much as you charge for that room - the market is tight, there is a natural barrier to entry and you entered that market at a more favorable time that now so your present day tenants have to pay you for the priviledge of living there because they have no other reasonable options.

That said, landlords can create at least some value and some do - for example my first landlord bought a large house and divided it into 1 bedroom apartments, in effect taking a dwelling from a market with lower demand and making from it 4 dwellings serving a market with higher demand, which is a way to create value, especially as he spent money on the conversion.

However the rents charged by landlords at present are almost always significantly higher than the value they create (if any), which is why in many places they actually exceed the cost of servicing a mortgage, so the landlord is really just exploiting having a better financial position (or even just better creditworthiness) than the tenant, as if there was no such advantage tenants would simply choose the cheaper mortgage over the more expensive rent.

(Even the mortgages themselves are much higher than they should be, as Price-To-Income ratios of realestate are 4+ times higher than the historical average all over the World, but that's a different discussion though I wanted to point it out because it shows the imperfections of said market: a highly competitive market would't stay so long above the historical relation between its prices and people's average income)

Also in my personal experience of 25 years and 4 countries, most landlords create little value: even good ones charge rents far above the little service they provide (basically maintenance, and often only because they're forced to by law) and the depreciation over time of the dwelling they're renting (which in the last couple of decades has actually been negative as even those houses getting older have gone up in price faster than inflation) plus a little profit.

Mind you, I've had mostly good landlords (sometimes both as persons and as landlords) and very few really bad ones, but that doesn't alter the fact that their profit from that business only comes courtesy of the low liquididity and natural high barriers to entry of the housing market and either a superior financial position or first mover advantage - their quality as persons and fairness as landlords don't change the inherent nature of the business they're in.