I think it is 100% due to pre-built OEM systems. The 2% or so of the market that is DIY is really almost irrelevant in the current market is all I'm getting at. And I would even agree that AMD has a good 50%+ of the overall DIY market. At the same time, I would say more than 95% of posters on this forum have DIY rigs. So basically, AMD is doing really well in the segment where 95% of people who post here are active, but that doesn't mean squat in the other 98% of the market.
In fact, I'd say the main reason to supply DIY supply chain has more to do with marketing - the DIY crowd and the sites like TPU, AT, Toms etc that cater to 'us' collectively - are very vocal. Just to illustrate, at this moment in the forums, look what the ratio of known users to guests is :
Total: 12,545 (members: 176, guests: 12,369)
I wouldn't even doubt that Rocket Lake for example, will mostly be sold to smaller SI's, retail DIY outlets, and the big OEM specialty rigs like Omen and Alienware. That's good for us no doubt, and would be a lot more than AMD has done with Zen 3, but I recognize it for what it is - halo products for marketing purposes.