Why http://download.opensuse.org/update/leap/15.3/sle/ includes all previous service packs?

Since SLE 11 (or may be even SLE 10) each service pack needs just two repositories - Pool and Updates (there were some deviations and of course this should be adjusted for each module but in general this holds true). I thought may be I forgot something so I installed SLES 15 SP2 (with subscription) yesterday and sure thing - the only repositories are those for SP2, there is no SP1 or SP0 anywhere. I do not have beta subscription for SLE 15 SP3 so cannot test but I would be surprised if it had been different. Why Leap 15.3 now suddenly has all previous service packs in its sle update repository? This is what seems to cause all those problems with patches for wrong SP.