Makes sense, though, doesn't it? Apple has >$150B worth of iPhone business that depends on the company delivering best-in-class single-threaded perf. Intel's PC chip business is worth ~$30B and its data center biz is worth >$15B.
These two are the only companies in the industry that derive a substantial amount of their profit from selling, directly or indirectly, systems with high single-threaded performance.
You could argue that Qualcomm fits into this category as well but its mobile AP business is nowhere near as large as these aforementioned businesses and the bulk of those APs are low-end and mid-range where the ROI for developing such fast MPUs probably isn't there.
Xeon is hanging with Power 8 in the multi-thread, multi-core, multi-socket performance too using less power. If that's the best RISC has got the ARMy have no chance apart from niches.