I agree. To explain further, it's easy as an outsider to call somebody else "lazy", but the outsider doesn't know how hard Id worked to finish Doom. Game development is famous for months-long crunch time death marches with 7-day 16-hour days. It's easy to say "you've been doing crunch for 6 months, here's another task for you: add PC speaker music" but it might be the thing that drives the game dev who has to do it over the edge. Are they being "lazy"? Are they just sitting around doing nothing, when they could be working on PC speaker music?
While it might have been possible to add PC speaker music, would it have been worth the effort at the time? How much would it have delayed the release of the game? Would anyone have cared very much about being able to have terrible quality music on their PC speaker?
Also all the sound stuff was outsourced! id hired Bobby Prince to make the music and licensed a playback library which seemed to have enough problems already with the supported sound cards. https://doomwiki.org/wiki/DMX
So they'd have had to extract this feature from a vendor where the relationship is already breaking down, or ditch it all and start from scratch with a new vendor, or inhouse code.