What truly causes rents to rise aside from supply and demand?

Every time rents increase, people say it’s just supply and demand, but that seems a bit too simple. I wonder what other actual factors are. Are things like interest rates, zoning laws, or big landlords actually major pieces of the puzzle, or are they more minor than people suggest? Basically, if someone asked you why rent keeps rising even when new buildings are being constructed, how would you explain it in plain English?