It is the reason why Singapore is different from the other countries in the region. There's no other way. As you say, why have rules if no one cares, not even those who should supervise respecting them. Once you strengthen control and fine those who don't want to understand, you'll get results.
The problem stems from education or the lack of it, to be precise. It's a no brainer not to throw the butt on the ground, if you want a clean environment. It's sad people don't realize what is at stake.