There's no point in buying an unrelated business that you're going to leave operating as usual - you might as well just invest that money on the stock market instead, or pay it out to your shareholders. So presumably if a company is buying a solution to X then it believes it can gain a competitive advantage by integrating X into the rest of its business.

Given that, I would've thought that the earlier you buy the thing, the easier it is to integrate it with the rest of your company and the quicker you start gaining the benefits of that. Waiting to buy the winner shouldn't be any cheaper than buying all the competitors in the field at the start, because it's no secret how everyone's doing. So the only reasons not to develop in-house from day 1 are if you're not as good at developing things as a small independent company, or there's some other advantage that you're missing, or the option value from the fact that small companies can go bankrupt on their own (but that's only really applicable if the business is capital-intensive).