I think the reason has been the fact of having an Achilles tendon issue, getting old and becoming steadily slower. But one must face facts, so here is the rest of the story--freshly number crunched:
The good years, when I could be very pleased with myself:
Year Miles Pace
2012 1,502.13 7:57
2013 1,571.55 7:58
2014 1582 1/2 7:55
2015 1573.61 7:57
The wheels are coming-off years:
2016 1451.9 0:08:04
Still pretty respectable, but not making 1,500 and over 8:00 for the first time...
2017 1077.38 0:08:23
Now, way below 1,500 and still slower: I think I was experimenting with fewer, more intense runs...
2018 866.36 0:09:09
Okay, low miles is not, I repeat, not working...
2019 1247.54 0:09:27
Okay, still slower, but a big increase in miles for the first time. This was the era of my monthly goal of 100 miles coming into effect. I had found that I felt less crippled with injury if I put in a bit more miles.
2020 1227.54 0:09:14
This feels like progress: I kept up more-or-less the same miles but did a better pace than the year before, for the first time--probably the first time since the first couple of years I've run. I took up running in 2002 and I think I hit a plateau around 2003 or 2004.