There are countless tools competitive with or better than what I use for email, and yet I still stick with my email client. Same is true for many, many other tools I use. I could perhaps go out of my way to make sure I'm always using the most technically capable and easy-to-use tools for everything, but I don't, because I know how to use what I have.
This is the exact dynamic that gives OpenAI a moat. And it certainly doesn't hurt them that they still produce SOTA models.
That's not a strong moat (arguably, not a moat at all, since as soon as any competitor has any business, they benefit from it with respect to their existing customers), it doesn't effect anyone who is not already invested in OpenAI's products, and because not every customer is like that with products they are currently using.
Now, having a large existing customer base and thus having an advantage in training data that feeds into an advantage in improving their products and acquiring new (and retaining existing customers) could, arguably, be a moat; that's a network effect, not merely inertia, and network effects can be a foundation of strong (though potentially unstable, if there is nothing else shoring them up) moats.
Yeah but the lock-in wrt email is absolutely huge compared to chatting with an LLM. I can (and have) easily ended my subscription to ChatGPT and switched to Claude, because it provides much more value to me at roughly the same cost. Switching email providers will, in general, not provide that much value to me and cause a large headache for me to switch.
Switching LLMs right now can be compared to switching electricity providers or mobile carriers - generally it's pretty low friction and provides immediate benefit (in the case of electricity and mobile, the benefit is cost).
You simply cannot compare it to an email provider.
It was pretty simple for me to switch email providers about ~6 years ago or so when I decided I'd do it. Although it's worth noting that my reasons for doing so were motivated by a strong desire around privacy, not noticing that another email provider did email better.
This is the exact dynamic that gives OpenAI a moat. And it certainly doesn't hurt them that they still produce SOTA models.