My read on the Altera acc was that Intel needed to shore up fab volumes in the face of their foundry customers jumping to TSMC first chance they could. As the capital required per node continues to rise exponentially, they need more and more volume to amortize that over. This is also why they're trying to get into GPUs again.
To slightly refine this, Intel didn't have many "foundry customers" before Altera. Via Wikipedia (https://en.wikipedia.org/wiki/Intel#Opening_up_the_foundries...), the need to fill up the manufacturing lines was engendered by poor x86 CPU sales around ~2013, not poor third-party fab runs. In 2013, Intel was still ahead of TSMC with 22 nm.
Didn't they also drag down Panasonic or something? I remember there being a lot of rumors of them being an extremely bad partner at the time, basically no technical support, unreliable capacity due to by core business and not giving two shits about the success of the venture in general.
