As others have said (one or three thousand times), dark blue trousers have (at least) two strikes against them when it comes to odd jackets - they look too dressy and they're a black hole.
They look bad when paired with a jacket because they always look dressy there really aren't any dressy looking odd jackets. Aside from the navy blazer. And if you're going to wear navy trousers with a navy jacket, they should match exactly. And have dark buttons. And it's easier to refer to that combination as a (lounge*) suit.
Plain navy doesn't really blend with anything else. It's too dark. You really have to accept that it's a high contrast look. That doesn't work well with odd jackets. The best odd jacket ensambles are warm and have a nice blend of colors that coordinate well.
Jeans avoid both of those pitfalls. They're obviously unmistakeably and utterly casual. And even when they're very dark, there's either some sheen or some variegation to the color. It's a softer color that's much easier to pair with a vibrant (or even a subdued) tweed,
* Where you at, Sator?
Most men don't are afraid of blue odd trousers because they simply lack imagination to wear them well. The trick as always with trousers is to get a combination where the jacket is same shade or darker than the bottoms. A pair of French navy trousers, paired with rust tweed jacket and navy blue hunting tie on tattersall shirt is a lovely autum combination. Think painting French navy with autumn colours- not navy sigh muddy brow - and you have a winning combination. For some inspiration try this