Most teams have components built by a handful of specialized external engineering companies. Some things are dealt with internally, but the lower order teams don't have the budgets to deal with much of the technology in-house. Ferrari is the exception and they do almost everything themselves (this might have changed because this was nearly 10 years ago).
The lower order teams get called "pit dodgers" (behind their backs). External companies know that statistically these teams don't finish so many races, and the attention to detail in the design and finish for these teams is much less than those premium teams receive.
It is sadly a vicious circle. Statistically, they will have worse drivers, who are more likely to crash or damage the cars early in the race, so often the cars in the lower order teams don't have the required staying power for the entire race.
I found it interesting to know that F1 cars have reverse gear, simply in accordance with regulations. It doesn't always work that well however, and I believe on one occasion its inclusion was overlooked.