Not so sure about that, Tegra may not have been the complete runaway success that NVidia would have liked or even have you believe it is, but I wouldn't say it is gaining zero traction.
The first couple of incarnations got in quite a lot of phones, loads of design wins, today the only design wins they are generally getting is their own. That is absolutely a lack of traction.
Problem is they burned the industry, promise a 3W chip and bring a 3.2W chip let alone a 5-6W chip and your design win(which is based on the final specs of the chip they are promised) turn into mothballed projects. When you have a 10-20 companies putting decent money into design wins of which only a few make it to market customers for your chips get wary. When the second gen does the same, you end up with less design wins each generation. Nvidia failed badly to turn design wins into final products, as a result getting far fewer customers with each generation.
When you move from announcing loads of customers at launch with loads of design wins to announcing a couple of your own products which are in a niche market with low sales... well, zero traction is fair. They've gone miles backwards from the interest they had from the industry since Tegra 1/2.
People don't trust them, MS and Sony reportedly refused to work with Nvidia again on a console. As with this thread, rather than work with the industry and their customers they've run around suing everyone and patent trolling.
Things like HSA are going to make mobile chips Samsung, Qualcomm or AMD offer for things like use in the car industry are going to leave Nvidia behind in technology and capability.
Car companies can ask any chip company to make a product made up of any IP blocks they want. AMD even provide this service directly with custom chip design. AMD gpu, ARM cores, their own IP block, it will mean different models can offer different versions of the chips, different capabilities using the same software. Can switch one gen from AMD, the next to Samsung without redoing all the software.
Nvidia has been boxing itself into the corner with Tegra rather than getting in line with the industry.