They spent what was required to survive the first year. As @midds pointed out there was nothing to sell to offset this. There was Ashley's for profit legacy which gave them that headroom at first. Then they got some real talent and made the Champions League. You are correct, they did fuck all in the last windows as they really couldn't. There may have been some mistakes in not selling in the last year but there wasn't anything high end to sell, right?
Let's see what happens this summer when there is some money to spend as it appears there will be. I also like the fact that Mitchell is buying young talent that just might translate into something to sell in the near future.