Why is it not compulsory to wear full leather protection while riding?

[ttaskmaster]

I've been riding for 22 years and never worn leather trousers before.[/quoye]
Fair point number one.

These were "nearly new" as in only used a couple of times but in the correct size.

With non-race leathers, I find the 'correct size' is the one that best fits to enable normal riding. With some, it will be actual size, but I find many are best going one larger, for that reason.

I don't really have the time on it to be breaking trousers in on the off chance they might stretch when I can just go back to jeans or get a pair of textile trousers instead.

Fair point number two.
It usually takes me about a week, but if you ride purely for leisure then obviously longer.
Out of curiosity, I did sit on a friend's Tiger last night just to see... Higher up than I'd be comfortable at, but still pretty nice!!