As a motorist I can see the frustration that people can get from being behind a cyclist who refuses to use a cycle path which is perfectly good , out of the way of traffic yet is content to hold up the flow of traffic .
There are far fewer "cycle paths which are perfectly good" than most motorists think. Now, I generally prefer cycle paths because I think it's more fun dealing with a 20% increase in rolling resistance (due to most councils using a less smooth tarmac than on roads) than a line of motorists behind me, but most of the examples of "perfectly good" cycle paths that come to my mind are not in this country!
Even the East West Cycle Superhighway (CS3) on London's Embankment isn't perfectly good: the surface is top notch and the signs are clearer than anything we'd seen before, but I suspect that all those traffic lights and their lack of coordination and countdown timers means that it's actually slower to use the cycleway than the carriageway.
Or the Cambridge-St Ives rail trail: smooth, wide and direct, but the level crossings make cyclists twist around and stop for motorists (or often no motorists), both end junctions are hostile unsigned messes and it floods near St Ives, which seems like an achievement when most of it is higher than nearby land.
More often, it's simply a case of it not really being worth dealing with the junction onto a cycleway because it finishes before you've recovered that deceleration and extra effort and almost always before it has helped you through any major junction. Some cycle paths are worth using IMO more because the alternative road is that awful (A17 Fosdyke Bridge, for example) but that doesn't make the path good: it's just less shoot than cycling on a truly awful road.
I asked for suggestions of decent-length good cycle paths about a year ago, in
https://www.cyclechat.net/threads/best-cycleway-in-england-for-part-of-a-tour.271330/ if anyone has some more "perfectly good" ones they'd like to suggest.