It's not surprising at all to see AMD drop in a Steam survey.
While other software is available on Steam now, lets be honest, its a gaming platform mostly used for gaming.
Well, Intel's chips are better in games.
If I am remembering correctly, even the new Ryzen 3000 showed to still be behind or next to the lowly 4/8 7700K. That's great that these chips have enhanced IPC and they look good, but until they game as good or better, these Steam results won't change.
While all the various benchmarks look good in a review, in all reality not many people care about encoding or file conversion, or multitasking, or file zipping performance. All chips do those things well these days.
Steamers want gaming chips over all.
You say 'lowly' 7700k, but that was a $340 chip new in January 2017! Nothing lowly about it, that was the very best consumer chip Intel put out just two and a half years ago. Can you even buy a used one for less than $200 now? That's how much a
new six core Ryzen 3600 will be.
Tests are showing that multithreaded and Ryzen specific optimisations are starting to impact performance positively in gaming.
Techspot here showed how much better the Ryzen 1600 now looks against a 7600k than it did 2 years ago. No doubt in no small part to the fact Ryzen's software support is maturing, and Intel's performance is actively degrading with every security fix in Windows.
The 7600k was a little faster in games back then,
now it's noticeably slower on many demanding titles showing a positive trend for more extensive multithreading in games, one you can expect to continue.
The obvious reason
why AMD's CPU share has slipped back in this survey is a great many number of people are holding back on buying AMD upgrades
because the Ryzen 3000 series are due soon. Count me as one of them.
What leaks and tests appear to be are showing are a bottom end Ryzen 3600 $200 AMD part is probably within 5 percent in gaming of a near $500 top of the line Intel part.
If this is indeed the case and there are another bunch of faster AMD parts above this base model, we definitely WILL start seeing significant changes in these Steam survey results in the coming year!