He had just been awarded a Triumph by the senate, but they decided to award it after the deadline for announcing one's run for consul so Caesar couldn't run that year. In response he renounced his generalship and triump and ran for consul anyways. Why couldn't he just wait a year?
This is pretty simple, though someone unfamiliar with the period wouldn't know it.
There's a prestige reason and a tactical reason. The prestige reason is because of age restrictions in place (certainly since Sulla reformed the government ~82 BCE, possibly earlier) 60 was the first year Caesar was eligible to stand for the consulship. Winning the first year you are eligible was the most prestigious way to become consul. Not winning that year amounts to a failure on some level.
Tactically Caesar wanted to run because his soldiers were there and could vote, and he was popular with them, and he was returning to Rome a war hero. The next year the soldiers might not be in Rome to vote, or their motivation might have cooled, and the people in the city might have forgotten the victory of a year ago. Caesar had a huge advantage in 60 he couldn't count on in a later year.
In addition he had things he needed to accomplish ASAP like getting Pompey's settlement of the East ratified and getting Crassus his tax break.
60 was the year Caesar was supposed to win, the year he was positioned to win, and the year he needed to win to get stuff done.