Sometimes it's worth looking at the why and the initial cause. It's a bitter pill to swallow from Cisco, but a bunch of the people leading Arista are ex-Cisco. In a few other cases, Cisco have typically left things to go bang - even after acquiring companies.
I'd expect the reason they're trying to litigate them out of existence is because they know the tech works and there aren't many working options at scale for Datacentre Networking at this kind of scale.
A different take
I think Cisco is trying to drive Arista into the hands of HPE. HPE can support the legal challenges much better than the smaller Arista. But if HPE borgs Arista, HPE will destroy Arista like it has managed to do with most other acquisitions. Anyone remember HP's H3C acquisition? That was supposed to be the end-all, be-all networking acquisition that would position HP to take on Cisco in networking.