[simias]

The size of the transactions is mostly a factor of how many addresses are included. So moving 1BTC split across hundreds of addresses ("dust" in the jargon) is a lot more expensive than moving 1000BTC from a single address for instance.

Unfortunately it's generally advised to use a new receiving address for every bitcoin transaction to make it harder to trace how much money you have and how you earn and spend it (most wallet craft a new address for every receive transaction) so it's very common to end up with your assets split up across dozens or even hundred of addresses.