The original ICAO standard ILS were based upon 2.5 to 2.75 degrees. This suited jets with slow spool up times and thus higher power needed to maintain the angle. VASIS were standardised to these angles back around the late Sixties.
Following usual pensioners noise complaints under glide paths the Sydney (Australia) runway 07 ILS was raised to three degrees giving extra height over the outer marker beacon. Raising the GP to three degrees made almost no difference to the noise foot-print but it made the local politicians happy that something had been done to counter the complaints. ICAO thought what a good idea and three degrees was adopted as the standard. In Australia it cost a lot of tax payers money to then standardise the remaining ILS and VASIS around this vast continent. I know because I flogged thousands of miles in the calibration flight DC3 as part of the job.
Again in the Fifties with introduction of fighter jets such as the Mirage into the Royal Australian Air Force the RAAF continued with a landing policy of touching down at the "piano keys" for fighters. This permitted more runway available in case of brake-parachute or aircraft brake failure due combat damage I suppose. I can only guess the current lower approach angle PAPI or VASIS mentioned in the first post is a relic of the old days where piano key touch down was considered the epitome of good airmanship (rightly or wrongly, depending on your viewpoint)