Some insulated multistrnd copper wire is pre-tinned and a lot is
not.

What is the purpose of pre-tinned wire? As far as I can see the
advantage is that the copper core doesn't oxidise which means the
wire can be soldered or fixed to a terminate with only minimal
cleaning.

Sounds like a good thing to me, so why isn't almost all wire pre-
tinned?

Is cost really so different?

Does the tinning-coating replace where copper would have been in
the overall wire and tinning is of higher reistence?

Is flexibility affected?