Can think of a few examples in Scotland.
East Kilbride is one of the largest settlements in the country (pop 75,000), but only has a half hourly service to Glasgow City Centre serving two stations in the town, both single platforms. Probably a quirk of being so close to Glasgow and effectively being a giant suburb - EDIT: And being on the end of a branch line. The aspiration is for 4tph I believe and doubling beyond Busby.
We also have Stirling, considered a city, but actually relatively small (pop 37,000) with 2tph to Edinburgh, 3-4tph to Glasgow, and even a twice daily service to London. But this has been because of its location (it’s historic importance was also down to this) effectively being a railhead first other towns in the vicinity.
Ayr and Kilmarnock both have roughly the same population (about 46,000) but the former gets 4tph to Glasgow as opposed to the latter’s 2, mainly due to the line to Ayr serving many other places of significance en route. The Kilmarnock line only really serves a handful of villages and Barrhead.
In the Glasgow area there are a number of small villages which get possibly generous half hourly services. I can think of Cardross, Howwood, Lochwinnoch, Bowling, Kilpatrick, Langbank to make a few. But offering that frequency probably makes the train more than twice as attractive than only offering an hourly service, for example. Their proximity to Glasgow also matters too, similar sized places elsewhere in the country wouldn’t receive such a service.