There are economies of scale here which are implied, but never expressly stated. For example, you may also ask the entirely equivalent question,
During The Siege, why don't they just fly up cloaked in all the
Jumpers, blow up the Hives with their combined drones (similar to what
we see against the asteroid field in S4 prem or S3 ending), and then
cloak again when not shooting? Even if they can't fire enough drones to kill a Hive, they could at least take out a large number of darts/blow up the launch bays.
The simple answer is that cloaking a Jumper has a non-trivial cost, which is never stated, but the character's suggestions regarding it imply it. In addition, it's clearly stated that Ancient cloaks and Ancient shields are very similar technology, and Rodney clearly states in 2x09 that they are not intended for long-term operation. The regular Jumpers are all brought back to Atlantis for servicing, recharging and whatnot, but Ford's never will be.
It's one thing to sit in a cloaked Jumper for a few hours, but the show never as far as I can see suggests using it for more than a few hours, and never suggests any tactic which would depend on more than this. In addition, the episode where Rodney gets sunk under the Lantean sea states clearly that the Jumper has a decidedly finite power supply, which Ford has no way to replenish without Atlantis. This leads us to conclude that
- Ford has to abandon the Jumper eventually, since it will run out of power.
- Ford would have to continually babysit the Jumper watching it's sensors to determine when he needs to cloak and run- he can't just leave the cloak on for funsies. This would leave him no time to do anything else. If he doesn't, it's a giant "PLEASE FIND ME" sign.
- We remember from the premiere that the Wraith are especially concerned with destroying or using any Ancient technology. It would attract a lot of attention. Ford on his own, however, isn't even worth sending a dart to feed on- if he was even detected.
In short, on his own, Ford can easily hide in plain sight in a human colony on his own. But the Jumper is a liability- he can't depend on it, he can't really hide it, and it's a giant sign for his enemies, and his friends, to find him.