I will tell you why most are biased against custom built pc's. Quality. It's just not there. You have a $2k budget. For that price you personally could build an amazing machine with top quality and reliability parts, of your own choice. Or, you could buy a mediocre pc of questionable parts and reliability.
They will tell you 'oh it's an fx990 motherboard' for instance, but what they won't tell you is its a Biostar, and the cheapest possible one, which costs them $40, but they charge you $119, and wont last but days longer than the warranty because it's so cheaply made. The psu is another bone of contention, 'oh it's a 650w gaming psu', made in Taiwan, of an unknown brand, sub part capacitors and an output so far beneath reliable power that a quality 430w has the same ratings for 1/2 the $97 price tag. The only component certified and guaranteed to be exactly what it claims to be is the cpu. They are either Intel or AMD and there is no way around them not being what they are.
Custom pc builders are in the business of making a profit. So they buy cheap, in bulk, throw a pc together, then charge premium prices to cover labor, storage, shipping, parts etc and still come out ahead, all at your expense.
Do your research, read the threads, make a tentative build on pcpartpicker.com, ask for advice, listen to the advice, change the build, buy the parts, and either build it yourself or take all the parts to a reliable shop and have them build it and you'll end up with a much better, stronger, faster, more reliable pc and still come out way under budget.
Or pay through the nose to get robbed.