These guys play at a different level altogether. You shouldn't worry about it too much now. First you need to master the basic odds etc. So just play by the pot odds now.

And to answer your question, the likelyhood someone has a good hand is simply smaller when there are 6 people than when there are 10 people. And if 5 have folded before you, your hand becomes "better" because you simply need to have the better hand out of 4 more people, instead of the best hand out of 9 more people if you were first up to act (UTG=under the gun). That's the general idea.

But do not confuse this with against-the-pot-odds raises etc you see on TV. There are different reasons why they do this. And eh, they don't know what cards are gonna show up.. they really have the same odds to get their "good card" as everyone else.