The Ryzen Zen 3 5000 family had a release date of Nov 3 to Nov 5 depending on which press release you listen to. Non Jan 5 2021 2 months later no one can obtain any 5000 series processors on any quantity..
Tech products just do not have a long shelf life. AMD obviously would love to sell everything they can while it's at the top of the game, but there's a whole lot going on that prevents them doing more.
So first, and obvious, is that launch demand is obviously very heavy for new CPU's and the entire supply chain is severely restricted. I've read articles on backups of semi's at distribution centers because they don't have labor available to unload them. It's affected more than just computing gear... I've not been able to get GFI/AFI circuit breakers for my home renovation project. I can imagine it's the same at ports where ships aren't getting unloaded in as timely a manner as before.
But on top of that, it could easily be AMD has tapped out their 7nm wafer allotment and options. TSMC just doesn't have the capacity right now to provide AMD with 7nm wafers for CPU's (and GPU's) for desktop, server, HEDT markets as well as GPU's and game centers. Speaking of gaming centers (PlayStation, XBox), they have solid multi-year contracts that will get serviced preferentially so that's where a lot of their wafer allotment will be directed.
The next most obvious priority to get 7nm wafer's is for server CPU's (Epyc, Rome). That has to be a corporate priority: take as much market share as possible while you can. Conservative data centers will be less likely to jump ship once Intel has got back to a performance parity so now's the time to get them embedded with your ecosystem.
Recent articles have indicated TSMC is charging a premium for additional 7nm wafer production, which only makes sense as more companies are going to them. Nvidia does too, for their 3000 series GPU's (I understand Samsung's 7nm process isn't working out so well for them). I strongly suspect that's the biggest bottleneck. Just not enough 7nm wafers to go around so something's got to give and it only makes sense the desktop market, especially the fickle DIY segment, is going to be the loser.