The whole system got reworked honestly. Valve made a lot of changes when they launched CS2 and it affected everything related to skins and trading. Not just how you buy stuff but also how collections work and what happens to your old CSGO inventory. This covers most of it pretty well https://historyofyesterday.com/csgo-market-vs-cs2-market-whats-the-difference/. Took me a while to understand what stayed the same and what changed completely. My friends were confused too so I shared it with our whole group. Once you get used to the new system it actually makes sense. Just different from what we all knew before. Worth spending ten minutes reading if you've been playing since the CSGO days