businesses that 'need to haul ass' usually still want to try something out before buying it. That doesn't need to a a free plan, but it's common to offer some trial period to new users.
Also totally OK if planetscale doesn't do this and that $39/month _is_ the best way to try them out, I just think it would be good for them to make explicit in the article what I should do if I think I might want it but want to try it.