I'm an arborist since 2022 in the UK and yes, never top trees. But...

There's three scenarios that come to mind in which it's somewhere between "acceptable" and "totally fine for some reason".

One, it's conifer hedge (the types popular in the UK) as these typically respond very well to being topped. It's what makes them a nice tidy hedge. I'm specifically referring to hedges above 3 meters in height. If you ever worked a hedge like this you'll quickly realise the topped stems are the platform to work off. These hedges can be maintained like this for years. For some reason, topped hedges are completely fine with being topped.

Two, it's either topping or removing. Arguably neither is ideal, but some retention is better than no retention. Topping puts the tree on senescence pathway and gives the ecology time to transition from alive to dead and dying. Whereas removal just makes the local fauna get confused about where the tree went.

Three, veteranisation in woodland settings. If there's a distinct lack of standing deadwood and age variation in a population of species in a given woodland NVC type, the topping and verteranising could be a positive management approach on a sample of trees.

This advice is very specific to the UK and especially on point three to the NVC woodland types. Generally though, prune properly at the correct locations, using proper technique being mindful of the structural loads and balancing of the tree. Topping generally, "because reasons" isn't an ideal approach at all.

> Topping puts the tree on senescence pathway and gives the ecology time to transition from alive to dead and dying.

Is this why the council recently topped a tree on my road that's been breaking up the pavement? We thought they were cutting it down since they dug up all the tarmac around it, but they just knocked the top off, taking something like 98% of the leaves with it, and then put fresh tarmac over the exposed roots. We've been puzzling over that for a week...