Exactly. I love open source software and use (and contribute to) it all the time, but the sad fact is that, despite the "many eyeballs" claim, most open source software is very rarely audited. I am willing to believe that KeePass is in fact implemented well and safe to use, but I don't actually know anything about the developer(s) behind it, don't know anything about the future development of the software (will it still be the same developers? Will new unknown people start contributing? etc), and pretty much the only thing that the developer(s) stand to lose by screwing up is reputation.
On the other hand, AgileBits (makers of 1Password) is a company, with actual money on the line (in addition to reputation) serving as an assurance that the product will not only continue to be developed, but will remain secure.
If KeePass screws up, some reputation is lost, people may switch to another product, and the developer(s) can just move on to working on other software if KeePass can't be salvaged. If AgileBits screws up, not only is reputation lost, but so are paying customers, depending on the severity the entire company might go belly-up (e.g. if 1Password is compromised heavily enough that it can't be trusted anymore), a lot of people are suddenly out of a job, etc. Basically, there's a lot more at stake for AgileBits, which makes it much easier to trust that not only are they going to do their job right, but they're also going to have processes in place to ensure a build never gets released externally that doesn't pass QA, etc.
And don't forget that as a paying customer of AgileBits, I can get support from them for any problem I might be having. Open source projects don't typically employ support personnel, and generally rely on the community to try and provide whatever support they can.
---
Ultimately, this comes down to the fact that this is a specialized class of software, where one breach can mean irreparable damage as the attacker now has access to your passwords for everything. For that kind of software, I really want the backing of a company, with a significant amount to lose, rather than just some unknown collection of open source developers.
Which is to say, for nearly any other class of software, I'm much more inclined to judge it based on its merits, and open source has a lot of advantages. But this isn't any other class of software.