The official UK singles chart is compiled and based on sales and Spotify like streaming platforms, beyond a person hearing a song and buying it because the like it, BBC Radio 1 & 2 have no actual influence over the UK Top 40 itself.
R1 and R2 and the local stations (most of which are ever so slightly horrific to listen to for more than 0.00001 of a second) have weekly playlists, usually labelled A, B and C. U2 would currently, most likely be on Radio 2's A or B List, whereas between 1983-2000 they'd have been on R1's A List. R2 plays the "older" acts now and for a while was the more listened to station of the two. Maybe someone from back home can confirm if that is still the case? Playlisting is usually: okay here are x amount of songs we the station/label wish to play (ie. the Top 20) and you'll hear the same variation all day unless you decide to turn off...
As to why TBT stopped at that dreaded #92 in anotherwise loyal U2 market to date? dunno, I imagine more fans would have bought an extended play whether physical or digital ala Depeche Mode's recent singles, though without the 40 remixes ffs. Say, three tasteful mixes of the song itself (single, acoustic, scifi mix) and/or maybe some live JT 2017 material over a couple of formats? Perhaps then it may have then charted higher around 25-30 on 'loyal fans' first week sales and in doing so, garnered more exposure.