Just because people say "ChatGPT" doesn't mean they actually mean ChatGPT. I drink "coke" from multiple brands. I've seen people say "ChatGPT" and then actually use Bard.
Being the brand name of the industry is powerful, certainly, but it doesn't mean as much as it sounds like just based on usage numbers.
The chatgpt site had 3.7B visits last month(#8 in Internet worldwide traffic). none of the other LLM vendors are even close.
You're right that there are people who say GPT and mean something else but the vast majority of LLM users are actually using ChatGPT.