Time Matters
It's easy to say "time is money" when you've got lots of money. If you're on a budget, though, it can suddenly seem like hours are a lot easier to come by than cash. For some quick and easy kitchen remodeling jobs, doing it yourself takes a few hours but really does save money. Go ahead, change out that hardware and paint those walls. For the big stuff, though, if you do it yourself it's likely to take weeks, not days, and that can add up to unexpected costs for you. Three weeks of eating out isn't saving you any money. If you can't finish a project in a weekend, it's time to find a contractor.
Equipment Considerations
Even if you have the time and the savvy to complete a project, it's also important to factor in the cost of tools. Many kitchen remodeling projects require heavy equipment like sanders and saws. Some of this equipment can be rented, but the costs for those you can't rent as well as the costs for smaller tools can really add up. If you find a contractor instead, remember that you're not only saving those tool costs, you're saving yourself a garage full of tools you're unlikely to use again anytime soon.
Professionalism
Chances are there's a reason you're not a professional carpenter, and that reason has something to do with your carpentry skills. If you find a contractor or multiple contractors to work on your kitchen remodeling project, you'll be hiring professionals instead of relying on your own presumably limited experience. While professionalism alone is not a guarantee that you'll love their work, choose wisely and you're almost guaranteed to find a contractor whose work is, sorry to burst any bubbles, better than yours.
The dangerous do-it-yourselfer inside you may yowl away at the sight of contractors in your kitchen, but if you're undertaking a big kitchen remodeling project, the beast will quiet down and thank you in the end.