As I see it, there was no need for the big 3 to develop touring groupsets as there didn't seem to be a demand for it. People were happy with their 8/9/10 speed triples, so why fix what ain't broken or if there's no demand.
Interest in mainstream touring and bikebacking was re-ignited fairly recently and out of the big 3, SRAM reacted the quickest, allthough with their electronic groupsets only, but we are talking BIG money for that. Shimano and Campag only do 1x for gravel and mtb.
Ratio Technology sells the internal shifter ratchet for 11 speed SRAM road/dropbar shifters. It replaces the standard 11 speed ratchet with a 12 speed ratchet that works with SRAM's mtb rear derailleurs, GX and up.
https://ratiotechnology.com/
A road double crankset of choice can be used on the front with a 11 speed SRAM/Shimano or 12 speed 11-51 Shimano cassette, with a standard HG freehub. Obviously if willing to spend on XG/microspline, there are more options.
This is the more 'affordable', mechanical, current tech, drop bar solution.
The alternative is friction shifters, you can run pretty much anything then. They seem to be available for drop bars as well.