More edges, more evaporation
A pot is surrounded by air. Its sides warm up, wind can reach the compost from several directions, and the root zone is smaller. Hanging baskets and terracotta pots can dry even faster.
The plant can be thirsty before it looks dramatic
Wilting is a late sign for many plants. Check the top few centimetres of compost, lift the pot if you know its normal weight, and look at whether water is running straight through instead of soaking in.
How to make a pot easier to manage
Group pots together, add a mulch layer where it is suitable, move delicate plants out of the hottest afternoon sun, and water slowly enough that the compost has time to absorb it.