The reason founder was that high was a long time ago towards the early days of the "everything is tradeable" update. The reason it dropped significantly is that more come to the market due to people unearthing them from old accounts. As much as I'd like to admit it doesn't exist, account trading still happens and I'd probably guess that people with old accounts who don't play sold them. Concerning founders specifically, since there's a lot less people playing twink nowadays, there aren't many looking to buy founders. It's as simple as supply and demand.

The same can be said about new update items. When the Halloween update started, NORMAL Asylum Shield was like 20m but as more people farmed it, it eventually dropped to it's Great Value price of 400k. Of course the price drop occurs much more quickly, because of all the people farming and the technically unlimited supply there was to be farmed during the update.

Now to address your idea of removing CS altogether, I think that would be a severe arrow to the market's knee because of the part it plays in our "Pocket Economy". If you buy something on CS, it's more expensive but you also get your item right then and there. If you put in the effort to seek out a buyer who's just looking for some quick cash you can find it much cheaper. To be frank, it's a nice balance.