One main reason is that WAVES is failing to build solid projects on the platform, that otherwise is a good one, quick, cheap, etc... But value is not only about technical considerations, but about community and projects.
Really? Most ERC20 projects I have heard of are purely hyped vapour. Many just used contract to create token to extract money from people sucked into ICOs - nothing 'solid' at all.
Many claim to be disrupting this, that or the other Industry - but, really, if by some remote chance one of these
did actually achieve the goals they hyped at ICO time or on their cut & paste template websites, the Ethereum platform just wouldn't cope. Hell! It couldn't cope with my occasional use!
On the other hand - I have come across some people, not into crypto and only heard of Bitcoin (but don't know what it is), that have heard of, or use RewardMob. Another gal, from Oz, who had heard of Incent, hadn't even heard of Waves.