I'm wondering what part of the country you're in, and whether the eastern side is very exposed, meaning there's no shelter from a large structure or trees on that side. Easterly winds are cold and often strong, and that might be why your plant chooses to grow away from that side. the other possibility is that there is shelter which causes shade, and wisteria will grow away from shady areas.

Not exposed at all, or shady. Full sun. South Staffordshire, in the lee of a hill. Very often the worst of the weather shoots over our little valley.
My brother had one on south facing wall and it grew both ways.
It has been there for 19 years but won't cover the bit of wall for which it was intended. I think I'll just have to plant one the other end and hope it grows west.

There will be an environmental reason why it refuses to go east, so as long as it's not something to do with the wall up which it's growing, planting another at the other end may solve the problem. be interesting to see if the next one only grows in a Westerly direction as well.