Why do Thai people use the "w" sound as a "v" substitute?

The Thai language doesn’t have a “v” sound. So, many Thai people use the “w” sound as a “v” substitute when pronouncing English words with “v”.

The thing is, they’re not close. “V” is formed by placing the lower lip against the upper teeth. “W” involves making a circle with the lips, then relaxing them. What’s confusing is, the Thai language does have an “f” found, which is much closer to the English “v”. (Try them all out in your mouth to feel the similarity.)

I’ve seen a variety of explanations online that make sense historically, but not linguistically (at least, not to this amateur). They range from: RTGS transliteration of Indian/Pali/Sanskrit-origin words that involve “v”, Chinese diaspora pronunciation of a combined w/v sound, regional dialects, and just plain “we were taught that w and v are the same”.

So why would a less-similar consonant be chosen over a more-similar one? Back down the linguistic rabbit hole…