Loss of Roman technology in post-Roman Britain | AskHistorians Archive Observer

For pottery, it appears that there was a shift from large-scale commercial production by professional potters in a few major production centres to small-scale non-professional production for local use. If you make pots constantly, a potter's wheel and kiln are very useful. If you make pots once every year or few years for your own family's use, then the effort required to make and maintain a wheel and a kiln can easily be more than the labour saved over decades. The effort required doesn't just include making the wheel and kiln, but also learning the skills - learning how to make and use a potter's wheel, and learning how to make and use a pottery kiln.

Whether or not it was a complete shift is difficult to tell. The potter's wheel made it to Britain before the Romans - wheel-thrown pottery was being imported from Gaul in the 2nd century BC, and was being locally made in the 1st century BC. Roman rule saw larger-scale commercial production, and a much large fraction of pottery was made with wheels (but some pottery was still hand-shaped), and a much larger fraction was kiln-fired rather than open-fired (AKA bonfire fired). The end of Roman rule saw a shift back to hand-shaping and open-firing, as part of the de-professionalisation and localisation of pottery making. However, wheel-thrown pots continued to be used. These are often assumed to be leftover pots from the Roman period, or if found without sufficient context for accurate dating, are simply assumed to be from the Roman period if of Roman form, or Anglo-Saxon if not of Roman form. It's quite possible that the potter's wheel and kiln continued to be used, on a small scale. With a closer look at the evidence, and avoiding simply classified all wheel-thrown pots as "Roman", it does appear to be the case. For the evidence for the continuation of wheel-thrown pottery into the post-Roman period in the Lincoln region, see

Caitlin R. Green, "Romano-British pottery in the fifth- to sixth-century Lincoln region", 2016: https://www.caitlingreen.org/2016/06/romano-british-pottery-fifth-century-lincoln.html

Why did pottery production shift from centralised commercial production to local non-professional production? Two things that would have contributed were a reduction in long-distance trade and a shift away from a cash economy. These two things are not independent - reduction in long-distance trade reduces the need for cash, and lack of cash can result in a reduction in long-distance trade (local trade can more readily continue via barter). We know that there was a great reduction in the circulation of coins, leading to an almost coin-free economy. This is sufficient to explain the de-professionalisation of pottery, and a shift from most pottery being commercially-produced wheel-thrown kiln-fired pottery to local-made non-professional pottery.