Wolfenstein and Doom's nature as shareware was much less about the Internet distribution but distribution by third parties on physical media. They were almost universally available on magazine cover discs and anyone else shipping CD-ROMs. IIRC even Blender magazine had at least one issue shipping a copy of Doom.

While id was certainly an Internet aware company in 1993 most consumers were not.

Keep in mind in 1993 a minority of households even had computers. A minority of those users even had modems. Even when they did have computers with modems connecting to a "local" BBS could still be a local toll call.

A copy of that month's PC Gamer was much cheaper than a modem and got you not just Doom but hundreds of megabytes of other crap. Cover discs were still a big deal even towards the end of the decade where home Internet access was more common.

As for the PlayStation, it was released in the Japan in 1994 and the US in 1995. Doom was released at the end of 1993 so it's contemporaneous with the PlayStation. The PSX had Doom-quality 3D games (including Doom itself) for a fraction of what a good Doom running PC cost.