They might surprise by keeping all Monterey compatible Macs for another year (and then presumably dropping the 2015 and 2016 together with MacOS 14) but I feel like they want to shed the workload created by legacy Intel systems as fast as they can without upsetting people. At least there will hopefully be a couple of years' security support for Monterey so that would carry my 2015 almost to the 10 year mark still under some degree of support. I suppose the 2015 was still quietly sold until the 2018 models came out, it would be interesting to know how many are still in use and whether that would sway Apple's decision at all. They seem to have remained popular throughout the TouchBar era.While you could be right, the termination of the support for the 2014 MBP was right on schedule as expected for age. It was discontinued in 2015, so it's no surprise it didn't get Monterey in 2021.
If anything, the late 2013 MBP got support for longer than expected.