Why is Twm Morys so Strict

Because:

A visitor might be forgiven for supposing that not much of the native character of Wales has survived intact until today, especially if he happens to be staying in a place where no Welsh is spoken. By the 1860s the omnipresent nonconformist chapel, though entirely, and proudly, Welsh in language, had put paid to the customs surrounding wakes and marriages and things of that sort, as well as folk-music and dance. The stories of the Bible had in large part taken the place of native mythology, even the fabulous lives of the Welsh saints, whose holy-wells were by now neglected or filled in, and whose Fairs (Breton pardon) had been abandoned or candiflossed over. But one indigenous craft or art that has continued down the centuries, in the wake, as it were, of the Welsh language itself, is Cerdd Dafod (“tongue-craft”), or strict-metre poetry.

from: A Poet Introduces a Welsh Metrical Tradition by Twm Morys