Because clinging to positive things leads to more greed, more mental instability and discomfort as whatever your cling to will one day disapear or change, making you uneasy. Enjoying your bath isn't the issue as it is obviously trivial, the issue is believing in chasing the pleasures/satisfaction of life which are all impermanent.
This is one of the 3 marks of existence : anicca, which means inability to maintain things to your satisfaction.
This will ultimately lead to constant rebirth, immoral acts, and rebirth in the lower realms, as you might be tempted to do immoral things to satisfy your cravings (if not in this life then in the next).
So basically, you don't want to cling to positive things too much because it will ultimately lead you to hell. The opposite is also true, it will make you closer to nibanna.
Your question is funny as it represents the typical samsara mindset, where one wants less of what one dislikes and more of what one likes.