Once upon a time a young company needed to devote significant monetary and human capital to building their software and hardware platform. Today, they can use open source frameworks and commodity hardware. Marketing once meant medium to big media buys, which had high entry costs and provided little to no insight into their success. Today you can literally buy attention by the individual customer, and enjoy a deep and detailed understanding of the success of your campaign. In addition the (relative) abundance of early stage investors means if you have an idea, you can bring it into reality with (relative) ease.
Innovation is so cheap that it doesn't have to happen inside a big company anymore. If a team gets bought out and cannot pursue a new opportunity, someone outside the company will step up and go after it.