TSMC refused to dedicate capacity to Apple as it would risk damaging relationships with other companies.
IIRC it was Qualcomm who asked for a similar deal and were also rebuffed.
It's unfair to blame those problems on TSMC - they have plenty of huge customers, and the likes of Xilinx and Altera who make some HUGE dies (FPGA logic isn't directly comparable to GPU but still). AMD also make GPUs and don't seem to have some of the problems Nvidia blame solely on TSMC (presumably that's what you're referring to).