This is mostly for convenience and transparency in case of tax change and checking if things worked out as intended. Changes could occur in the future where, say, MS hosts an event dedicated to a no-tax weekend with the goal of raising a pool of some kind for another event (dumb example ik), or any modification in taxes and rules in the near future that might be enforced after the new market has been tested. There already are warnings for the tax whenever migrating items from the old market, with an indication under buy/sell orders where the input prices change according to the tax, but it never stated the tax anywhere there as far as I can find.

Even if there are no plans to do so currently, it still helps with keeping track of what the current tax is without having to dig for it in the News/Items threads; for players who have not been around this year, coming back to see the market overhaul with tax would result in confusion, as there is no indication of the tax amount until you either work it out yourself, or that you find this by-then-burried thread months or years later.

Multiple platforms with established marketplaces show such information on the dashboard or main page to avoid issues with hidden fees and falsified taxes (Marketplace.tf's 10%, DMarket.com's 1%-7%, CS.MONEY's 4%-7% and list goes on) which have been present in some gambling websites as they hide it in their TOS (won't name any due to obvious reasons.)

tl;dr - showing tax % under market = transparency, new and returning players will not be as confused and no "shady changed tax" thing.


P.S: That implementation was fast, well done sir.