There probably wasn’t much time spent building the case. Generally solicitors aren’t involved in these cases because it’s not possible to reclaim legal costs, regardless of who wins. Instead most people just represent themselves, and companies will often just send a local manager to represent them. So super low stakes legal process, where in the worst case scenario your out of pocket for the filing costs (£70) plus reasonable expenses for the other party (travel costs, lost earnings etc) which are all tightly capped, so unlikely to more than another £100-£200.
If this went down the small claims track in the UK then ASUS wouldn’t bother with a lawyer because you’re not allowed to reclaim legal costs in the small claims court. So unless ASUS thinks they’re gonna see a flood of similar claims happening, then the cost of a lawyer would probably be triple the cost of settling, or even winning the case.
Also class action cases are very rare in the UK. In the past the courts have generally refused to approve class action cases. It not like in the U.S. where there’s a cottage industry around class action cases. I’ve personally never heard of a class action case happening in the UK, I know they do happen, but they’re so rare that they don’t make it into the news, and most people will never involved in one either directly or indirectly.
I would bet that neither small claims or class action is possible in the US because ASUS has a forced binding arbitration clause in their End User Agreement that almost no one read when they activated their phones.