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Sram Electronic/Hydro kit have only two options (flat and post mount), sold indeed in distinctive box, while chainsets and cassette are three each and considered add-on, all cross compatible so it would make it impossible to offer a package with all these options.
Shimano doesn't care and doesn't sell full group sets, it's up to retailers to find individual parts and offer them online as a complete group or di2 upgrade kit only.
I agree though, it is annoying that shops use pictures of complete AXS group sets when they are only selling shifters, brakes, derailleurs, batteries and charger.
£2,300 is the 2x system RRP without mechanical parts (chain, cassette, chainset and bb),
With these parts included (excluding BB) RRP will become £3,315 and with PM £3,760.
1x setup will be around £600 cheaper.