1) I think Sigs are perfectly fine pistols.
2) The OPs question practically begs a subjective answer.
3) Sigs likely aren't as popular as many striker fired pistols because striker fired pistols are generally easier to shoot well and/or learn to shoot with. That doesn't make non sig folks or new shooters "lazy" it makes them practical. There is a difference. If you shoot a bad guy with a Glock 19 versus a Sig P229 there is not a heck of a lot of difference as far as the bad guy is concerned.
Characteristics of good striker fired pistols like Glock that make them appealing:
* Many local LE use them (right or wrong people tend to want what they see local LE use)
* Lower bore axis. Practically speaking hammer fired pistols will always have a higher bore axis than striker fired pistols. That's just physics. The lower bore axis is going to mean less muzzle flip and easier recoil management. That means more comfort, less flinching, more likely to be accurate for new shooters. More accuracy and comfort to shoot means more fun and more likely to not be discouraged. It also tends to mean lower times in competition.
* Consistent trigger pull on striker fired pistols mean they are easier to learn to shoot well especially in timed competition. Many new folks start out in something like IDPA with there fancy new DA/SA Sig, they suck and want to improve. So they look around see lots of folks better then them with striker fired pistols and realize life would be easier if they don't first have to overcome the inconsistent trigger (and the higher bore axis) and decide to give Glock a try.
* Price is an obvious reason as well. Others have discussed this already.
* Competitors like HK take market share. In similar price points.
* The grips are a little big for some folks. Length of pull being long in DA combined with the large grips (even the "E" models) mean for folks with small hands Sigs tend to be tougher to be as fast as with many striker fired pistols while maintaining good consistent trigger control.
Yes pretty much any/all of the differences between the Sig and Striker fired pistols can be overcome with enough training (more for some than others) but I'm sure many folks simply make the decision to pay less for a firearm that is basically just as reliable and that is actually easier to shoot well (and learn to shoot well) for practical reasons.
All that said, I'm a fan of Sigs.
The test of a first rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function. -F. Scott Fitzgerald