There were very few Chinese restaurants where I was living in the UK as a kid in the 1950s and early 60s, and almost no Indian restaurants at all. Then, the Chanticleer opened in Chester's Rows, and the gates of paradise opened! Dad had been in Hong Kong at the end of WWII, and stayed on for 3 or 5 years, and had told me that the food there was wonderful. It was my birthday treat to try sweet and sour Pacific prawns that first time, and the memory remains with me some 60 years later. Similarly, Mum had completed her nursing training at the Manchester Eye Hospital when Dad was in HK, and she adored Indian curries - the hotter the better. She would talk about Manchester's Koh I Noor restaurant long before any opened in North Wales. I couldn't wait to try this exotic fare either.
The point is that when I eventually tried both cuisines, I enjoyed them tremendously, but they were very much an occasional treat. Years later, I lived just two or three miles away from Manchester's famous "Curry Mile" but only went there a handful of times in 28 years! I ate at many different Chinese and Indian/Bangladeshi restaurants throughout the UK during that time, as well as lots of Italian, Spanish, Mexican, French, and even the odd British restaurant too, and rang the quality changes too - taking in the old Wimpy bars, KFCs, McDonalds, Milk Bars, Kardomah coffee houses, local chippies, and some very grand Michelin starred places too. Yet none of them were places that I went to every week. Many of them were a novelty - such as when visiting relatives in Toronto. They seemed to think it would be a real treat for me to visit some British themed "pub," when all I wanted was to try authentic Canadian fodder (if there is any, and Wendy's doesn't count!)
Why should Thai people be any different? Brits eat British food most of the time, with the occasional foray to foreign restaurants (more commonly now of course, due to the popularity of foreign holidays - despite which think of the Spanish Costas and the signs there advertising "Full English Breakfasts" and "Fish and Chips.") In the same way, lots of Thais will eat some Western food - mostly when dragged there by their Farang husbands, but sometimes as a novelty choice, and sometimes simply because some like the taste and the difference. I can't think of any Thais who would eat Western food for every meal if given the choice, just as most Brits wouldn't eat Chinese or Thai food all the time.
It's probably that degree course I took in "Stating the Bleeding Obvious" that led to the above, but the popularity of Thai food in the UK is probably no greater than the popularity of Western food among the Thai communities over here. It's a niche market. It might be growing, but - here in Surin anyway - there is definitely a glass ceiling for Western eating places. IN places like Bangkok, it is undoubtedly "cool" to eat in Western style places. Even in Surin, the popularity of Starbucks is quite remarkable - though most of the clients are either Farang, or rich Thais who want to be seen there rather than in some typically Thai places despite the +300% prices.
I've been asked to cook a variety of Western dishes over here by Thais, and most have enjoyed them. Several have asked why I won't open a small restaurant specialising in those dishes. Not a bloomin' chance!!! And the main reason is that I don't believe that tasting them once would make the Thais come back regularly enough to make it a worthwhile and long-term venture. As many have asked: "How do you become a millionaire in Thailand?" Answer: "Start with 2 million."