I completely understand what you're saying, but the problem is that if both guys are mediocre, and both have varying upside/downside, and neither is the QB of the future, it makes way more sense to stay with the guy who you know, the guy who knows the system, and the guy who costs half as much. The variables here are overwhelmingly against the Bears' decision to get Glennon. The Bears essentially spent twice as much on a car that might drive a little faster, but also has a better chance of breaking down.
What's more, they could have offered Hoyer more money and blown his socks off, then spent the rest to put the nail in the coffin of the Gilmore proposal. Instead, they got Glennon and were apparently cheap with their offer to Gilmore.