A Ford Focus - hardly what most would consider an outlandishly massive road-hog - is 1825mm wide (without the mirrors) and the normal width of a parking space is 2400mm. In millimetres, that sounds like a high number of clearance, but if everybody drove a Focus and parked perfectly in the middle of their space, that still only allows a total door-opening space (i.e. the clearance across both spaces) of 57.5 cm or 22.5 inches.
Bearing in mind that many people do not park carefully in the exact middle of the space - and that there are lots of average family cars that are wider than a Focus (along with the larger vehicles such as 4x4s, MPVs, WAVs of all kinds, vans etc., of course), it's totally understandable why it's a common problem.
I think the issue is that, with the size of even the smaller modern vehicles being wider - and don't forget that this will at least partially be a result of improved safety standards since the cars of decades ago - the standard space is based on the expectation of a reasonable level of youth, health, able-bodied-ness and various other factors that simply are not the experience and privilege of many, many drivers and passengers.
Keeping the standard minimum allowable space at the same width, on the basis that 'quite a lot of people' can manage with it is as absurd as closing public toilets and replacing them with street urinals, with the 'justification' that 'a full 50%' of the public find that them practical for their use, so who gives a stuff about the rest.