you don't want tail wind, that's slower than full wind to the sides.

note how the sailing ui has a color change to the ring where you are using wind to sail.

the bright green areas of that ring to each side are where you get the most speed.

as for why it's always against you, it's because the winds change with time of day and are determined by the valleys you sail through just like in real life.

tides change, and with that the winds.

so at one part of the day you will notice the wind going away from your docks, and at another time will be heading back towards you.

this is why picking the time to sail is important, because if you start when the wind is against you you will have a bad time.