[ryan_lane]

Because landlords are a business providing a service, and doing business has risk. Part of the risk around having a tenant is that they may have financial issues and may not be able to pay you on time. If you can't handle that risk, because you rely on the tenant to pay your mortgage, then your business isn't viable. Any business that relied on accounts receivable to be timely would almost certainly be out of business in a short time period.

Try doing consulting work and see how long it takes businesses to pay out your invoices. Be a B2B company, and see how long it takes businesses to pay out your invoices. Are they going to be willing to pay a late payment fee? Ask your accounting team what their average payout time is for accounts receivable.

The difference between these cases is power dynamic. Landlords have extreme levels of power over tenants. If it's legal to charge a fee for a late payment, the tenant either has a choice of paying a fee or having no home. It's an unfair balance, and the government shouldn't allow this to exist.