The UK is also at the beginning of post-Brexit trade negotiations with the US trade agreement being a central one. This is going to be part of those negotiations going forward and is all part of the governments strategy.
The US will be looking for the UK to pay US-style inflated prices for pharmaceuticals, change food safety standards to accept subsidised US farm produce, and install an ISDS court to protect corporations' anticipated future profits.
Compared to these, banning Huawei - which isn't even a British company - would be a trivial concession.
The current UK government is going to get bent over and given a reminder of BoJo's days at Eton before they get any trade deal from the US, and that is before you start to ask questions about internal US politics and the chance of passing any sort of trade deal during the coming election season. Humiliation is a baked-in assumption regarding any future deal and having some chips that you can afford to sacrifice during the deal-making is something worth keeping around if you can.