One of the main reasons for the Lee Enfield's longevity was the aversion of the British Treasury to automatic weapons because of the cost of, what they regarded as, "wasted" ammunition. The Sten gun which was an alien 9mmm calibre , only came about as the result of so much ammunition being captured from the Italians in the Western Desert. Confronted with the problem of disposing of it, some bright spark decided it was cheaper to fire it back at the enemy.It's a war pattern, delete any unnecessary work to get what is needed into that hands of those who needed them.
That is why there are so many variants of something like the Le Enfield! Makes collecting them a interesting hobby! I used to have a few myself but circumstances dictated that I sell them.
As a result, the Sten was invented, and allegedly produced at a cost of one shilling and ninepence each, it served its purpose but was possibly the worst and most unreliable weapon of WW 2.