<<There are technical reasons like radio service volume>>
Not sure what that means??
During early mornings at Heathrow pilots would sometimes ask for "direct to the FAF", particularly on westerlies when they were inbound from the North Sea. We could let them do it for a while but then had to give radar vectors to ensure they complied with the night noise requirement that aircraft had to be established on the localiser at least 10nm from touchdown.
I don't know what happens nowadays but that is presumably still a problem at some airfields.