The data aren't entirely conclusive. My sales increased but I can't prove it was due to the new design.
I could A/B test the old design against the new, but my sales volume is low enough that it could take weeks before we get compelling results for any experiment.
It's easy to come up with lots of ideas for design improvements, but it's much harder to actually implement them and then measure the results.
You look at the data. If you think the increased sales are due to the site redesign vs some other variable - well there's your answer.