The toilet is a place where human waste is deposited and this needs to be clean.
We go to the toilet all throughout the day and before and after sleep and during sleep. Sitting on dried wee, or witnessing a non-flush, or hairs and dust and bits of faeces, in and around the toilet, is just gross.
A toilet brush is one of the cheapest things to buy and basic toilet cleaners are not expensive either. There is no point putting a fancy toilet bowl cleaner and thinking it will do it all – some human intervention is needed also! And yes the bowl is meant to be white!