Yeah, main problem is that sigron don't actually compete in the same playing field as canon. There's not many standout lenses from either of them that are actually better in every respect than their canon counterpart, and compete decently on price too.
There's a few standouts, like the Sig 50/1.4 that have a direct equal.
The Tamron 17-50/2.8 may have good IQ for the price, but there's no IS. And the one with IS can't compete with the EFs 17-55/2.8 for IQ.
But besides those and a few others, the 'direct equivalent' lenses from sigron aren't up to the canon version, so people like me wouldn't buy them no matter how cheap they were.

I do like how they push the envelope in other areas though, you can get 3rd party lenses that there just isn't a canon equivalent.
The Sigma 8-16 is wider and Tokina 11-16 is faster, both beat the EFs 10-22 for the money, but the EFs has a lot wider zoom range.
The Sigma 30/1.4 I really wish had better IQ wide-open, because then more people would buy them, then canon might realise that there's a market segment unfilled and start building their own EFs primes.

Zeiss and Samyang also produce some nice glass, but they're both not in the same class as the canons because of the MF.

Then there's the überteles, the tamron 200-500, sigmonster 300-800, or siglauncher 200-500 f/2.8. They may not be as good as the canon primes, but they're the best at what they do because they're the only thing available at what they do. (technically, even the sigma 20/1.8 is "best in class" below f/2.8. scary thought)

What i'd be hopeful of is that sigron actually go head to head with canon for the same lengths and apertures, but actually also for build quality (i've seen a few lately that have been getting weathersealing), AF speed, AF reliability, but most importantly manufacturing tolerances and QC. Even if it means that the lens is only 20% below the canon instead of 50%, that will give canon more competition to reduce prices...