What could possibly make my left shoe develop leaks so often?

It's happened again, I've come back from a walk in the (light) rain and the left shoe of my current pair has just sprung a leak. This seems to be part of an annoying trend over the past several years, where after 2 to 5 months of buying a new pair and wearing them about daily at a primarily office job, the left shoe will develop a leak. The right shoe always emerges unscathed. I'll always avoid puddles if I can help it, so it seems as though the water just gradually seeps in as I walk. If I can get back home quickly, I try to dry them out, but sometimes they develop a mildewy smell and it's just never the same again.

I have a few theories, but none really convince me:

• I walk fast, am left leg dominant, and my left foot is ever so slightly larger than the right. Maybe more strain on the left shoe? The sole does end up slightly more worn than the right.
• But the same shoe size still comfortably fits both, so is there even a solution to be found?
• People travel on the right where I live, maybe there's an asymmetry of the walkways?
• I'm cheaping out and can't justify buying shoes over $80. In half of the cases, I notice the sole starting to separate from the upper part. But again, why the left in particular and why only these past few years?
• Or I'm meant to wear heavy boots. The only kinds of shoes that have escaped this fate in recent years have been my snow boots and steel-toe boots, which I wear almost daily in the winter.

Would be interested to hear any similar stories or better reasons from those more knowledgeable about shoes and shoe defects than I am.