Bike bottle interior coatings are not very durable. They're OK for a while if you only drink water and do not scrub the inside with anything abrasive at all. But one good scrubbing with a stiff brush and a few days drinking juice out of that thing, and it will taste bad, probably until you throw it out.
Most people want their bike bottles to be squeezable, so some tradeoffs are made. Everyday bottles can be rigid, so stainless steel (or glass) makes more sense.