A clean room can hide how recently it required someone’s sustained attention.

Cleaning is the rare work whose success is invisibility. A tidy room shows no sign of the two hours just spent on it, and because the result looks like an absence of effort rather than a presence of it, the labour is easy to overlook and easy to assume happens by itself. Whoever does it repeatedly knows this. It is one of the reasons the work feels thankless even when nobody intends ingratitude.

If someone keeps a space you share, say specifically what you noticed rather than thanking them in general. And if you do it yourself, saying how long it took is not complaining.