There are a few reasons why general contractor can be unreliable. One reason is that they may not have the necessary expertise in a particular area. For example, if you need a contractor to install plumbing in your home, you would hire a plumber, not a general contractor. Another reason is that contractors may be overbooked and unable to complete your project on time. This can be especially frustrating if the project is already underway and construction has stopped because the contractor has run out of time. Finally, some contractors may simply be unethical and take advantage of their clients by charging high prices and then delivering low-quality work. It's important to do your research before hiring a contractor and get references from past clients.
The short answer is that because they can be. General contractors can be unreliable for a number of reasons. Sometimes it's because they're overworked and don't have the time or crew to do the job properly. Sometimes it's because they're underhanded and take on too many jobs then subcontract out the work, which means that they're not responsible if something goes wrong. And sometimes it's just because they're incompetent or careless. The best way to avoid dealing with an unreliable general contractor is to do your homework before you hire one. Get references from friends and family, check reviews online, and make sure the contractor is licensed and insured. If possible, see examples of their previous work. And always get a written.