Garter straps with jodhs??? Haven't seen those since the 1930s LOL!!!
Jdhpurs are often worn with straps under the instep (either stitched-on elastic, which often fit inside the boot under the foot, or clip-on - called Joddy Clips - which go outside the boot) to stop them riding up above the ankle.
The fashion for baggy breeches originated in India, I believe, in the late 19th century, because they were cooler in the heat. It became a fashion thing after that and was often taken to such extremes some looked as if you had a pair of wings on your legs.
Earlier men' breeches (particularly British cavalry officers) were worn skin tight. They used get a close fit with the deerskin type by sitting in a bath of water and letting them dry on, like shrink-to-fit jeans. Nothing like a well-shaped thigh to turn a young lady's head ;)
Modern breeches aren't always close fitting above the knee, even nowadays. I've a Caldene pair with pencil pleats at the waist which have a bit of room.
'Britches' is the correct pronunciation of 'breeches', like 'throatlash' (correctly spelt 'throatlatch'). Sorry, verona, there's no such British word - it's just that many Americans incorrectly pronounce it 'breaches' :)