When roads and pavements are designed they take into account parking, flow of traffic and anything that could block it.
I know because I work with engineers who design roads and parking whose plans have to be approved and meet strict guidelines by transport authorities and the council who typical own the roads. Unless its London where some roads are owned by TfL.
So your talking rubbish. On my road parking is done half on pavement and half on road as sign posted, further down where the road is wider its park on the road fully. This was designed to allow traffic to flow smoothly through thr difference in road widths and still enable people to park.
You and your engineer friends might be very smart, but you can't have travelled very far in the country at all if you've never encountered a residential road with room for traffic going in both directions, but which always has cars parked along one side, allowing traffic in only one direction at any one time. I've lived on one for nearly two decades, but I must still be wrong in believing my own eyes and experiences, eh, as I'm apparently talking rubbish....
You do realise, don't you, that there are a huge number of residential roads in this country which have been there for many, many years - long before your engineer friends (or their parents) were even born?
Even on your own engineer-designed road, it sounds very strange and nonsensical for them to have deliberately decided to put pavement along half of the section designed specifically for parking. By 'design', do you mean 'make the best of what's already there'? If so, there are tens of thousands of residential roads where there simply isn't space to allow for lots of on-street parking and free-flowing two-way traffic.
I fully realise that a great many people have nowhere else but the public road to park their cars. That's fine, but IF they didn't need to, a whole load of roads would flow much more freely.