At the beginning of ride sharing, people believed there was absolutely no geographical moat and all riders were just one cheaper ride from switching so better capitalized incumbents could just win a new area by showering the city with discounts. It took Uber billions of dollars to figure out the moats were actually nigh insurmountable as a challenger brand in many countries.

Honestly, with AI, I just instinctively reach for ChatGPT and haven't even bothered trying with any of the others because the results I get from OAI are "good enough". If enough other people are like me, OAI gets order of magnitudes more query volume than the other general purpose LLMs and they can use that data to tweak their algorithms better than anyone else.

Also, current LLMs, the long term user experience is pretty similar to the first time user experience but that seems set to change in the next few generations. I want my LLM over time to understand the style I prefer to be communicated in, learn what media I'm consuming so it knows which references I understand vs those I don't, etc. Getting a brand new LLM familiar enough to me to feel like a long established LLM might be an arduous enough task that people rarely switch.