Let's look at two possible scenarios.

1- Size does indeed not matter in any quantifiable sense to Jedi, and they have nigh unlimited power capable of easily slinging the Death Star around. All through the Star Wars saga Jedi refuse to use these powers because apparently, they are stupid.

How many times have we seen a Jedi drop or otherwise lose his light saber and not instantly retrieve it with telekinesis? That should be an extremely simple task, and indeed it is one that is often seen done, yet there are examples when they either don't do it at all, or wait a long time to do it. For example, when Anakin drops his light saber in AOTC (while he's on top of the flying car), he doesn't pull it back at all; and he was in a situation where he really needed it. He wouldn't have gotten it back if it hadn't have been for Obi-Wan miraculously catching it.

So yes, apparently they are stupid, which is what I was getting at in the first place. That's the problem when a writer makes his character too powerful; it makes them look stupid when they are in dangerous situations and don't use their powers effectively or at all. Since you need dangerous situations for a story of this type, you need to place limitations on their powers in order for the dangerous situations to even seem plausible; i.e., not make the character look like an idiot.

There are plenty of other examples too. Why didn't Obi-Wan use the force to nudge Jango Fett's ship; or at the very least, the missiles that were tracking him; into an asteroid during AOTC? Even if you want to speculate that the series established a limitation on the size of objects that can be moved with the force (which it actually didn't establish at all; quite the opposite in fact), we know that a small fighter craft, and especially, smaller missiles, can be moved by a Jedi.