Disguise. He doesn't have an army anymore and isn't dead already, so the Autobots and humans will be looking for him.

 

Maybe he thought he could get Tina Turner to ride in him.

 

In raegards to Megatron's bio, and what you said originally, I think NEST only had the technology to see what was a Transformer or not with the heat signature camera used by Epps in ROTF. I don't think NEST has the capabilities to scan the entire planet at once and pin point the location of every Transformer on Earth. Plus, perhaps he took on the truck form to through his pursuers off? Right now, the Autobots and the humans know Megatron to be able to transform into Cybertronian tank, not a truck. So while they are busy looking for a tank, Megatron can easily drive by undetected.

 

I don't now about you but if I were an autobot and saw a tanker with spikes shooting out of it I probably would have attacked it.

 

And when it turned out to be nothing more but a truck with spikes on it and you just murdered an innocent human or two, you would have made all the Autobots look bad. That's profiling my friend. Way to get kicked off the planet!

 

It is always possible that the truck he scanned for the alternate mode already looked that way?

 

I wouldn't of attacked the humans if I saw any. I think megaton would have transformed anyways before I could do any serious harm.

 

Lol. There's a new one...Cybertronian Profiling.