Its because the sb riders like to ride down the line Richard. In a cross on breaze they may peel 2-300 meters downwind. To get that back they have to tack way the hell out to sea and back again. Or do multiple shorter tacks which is a pain on a surfboard.
Now today afterwork i'll find myself at a premier wave spot 20-30 knot cross shore. point break 3 meter set wave face.... oooh yeah. and it cleans up very nicely. I will think of Nico and i'll ride my TT deep in the pocket, drag my hand in the wave face..... I'll then blatantly avoid the pocket and ride upwind on the wave face and boost of the wave lip on the wave back out......
Multiple shorter tacks is NOT a pain on a surfboard - but for me much more fun than on a TT, as you can either jibe or tack or do an aerial transition/tack and get the good feel doing that
If you ride a half kilometer or more downwind, most will typically take really long tacks when they go back upwind, no matter what type of board they ride
It is a very "natural" thing to do (or natural lazyness ?)
Some take huge long tacks, others take more reasonable ones - personal preference and also how skilled you are to some extent when talking about directionals
(as beginners take longer tacks because they can not jibe nor tack)
I personally take short tacks often - as then you dont get as far away from shore, and IF a huge set rolls in, you can ride it (if noone comes from upwind), and you can also see your mates riding waves downwind - it is awesome to see a good friend whipping a top turn and see the spray from the outside - especially if the sun is from the right direction where it turns into a sparkling beatiful view
Short tacks are great on surfboards IMO, and I dont see any difference in the "length" of the tacks, apart from directional newbees who has'nt learned to jibe/tack well yet, and that is also fine of course