Intel is now going under because of the very fact that they still do all manufacturing in house. The price of Fab/Node research is existential to maintain. Intel ultimately could not support the research, and now they have seriously fallen behind AMD.
But you might have misunderstood my other statement about supply. The actual components that go into producing the microchip (Silicon, transistors, packaging... all the core components necessary are now in short supply world-wide. This means Intel is just as affected as someone like TSMC. Probably more, considering TSMC's market share in microchip production.