It is pretty uncommon for someone who has been self-employed for less than two full tax years to be able to get a mortgage based on those earnings. Your prior compensation doesn't mean much to a lender even if it was the same type of work. Even a shift in compensation structure say from being salaried to base + commission can be an issue when you're trying to get a loan.
They want to see that you can keep your business going in the long term because of the high failure rate and to ensure that you earn enough over the course of a year to pay given how sporadic self-generated income can be. Having two years' of data also allows them to calculate an average annual income. That's what they normally base your loan on.