Lots of reasons

45% of Scots want to be independent from the UK and this has a lot of effects.

The vast majority of people who want independence for Scotland also believe Scotland really needs to be part of the Eu in order to succeed outside of the UK.

These people also tend to blame all of there problems on Westminster and being part of the UK rather than on migration and being part of the Eu

The main pro-independance party - the SNP - has a large number of members and a very devout following from the 45%. Therefore when they said that Remain was better for Scotland, most of their voters and members agreed immediately.

On top of this - Scotland is politically far more left wing than England and Wales - they tend to vote Labour and Scottish Nationalist Party - both pitch themselves as left wing. The pro Brexit campaign was generally viewed as (and for the most part was) a very right wing campaign.

These are just a few reasons I can think of, I'm sure there are others - maybe Scots just decided that if the head of the WTO thought Brexit was a bad idea, it probably was.