I agree, or agreed, until I wrote a few dizains and then later became enamored with rondeaus and sonnets. I know tankas aren't supposed to use end rhyme but sometimes it's fun. Only recently did I expand to free verse.

I wrote a fun poem about my poetic journey from haiku to tanka and onward a couple of years ago, but before I discovered rondeaus and sonnets. You might enjoy it. https://medium.com/evolve/awakening-and-evolution-of-a-poet-69912862249c