No, I'm sorry - I think you are still misunderstanding the point of the signs.

There are people who want to try to enter the UK illegally, and they want to be undetected. Presenting either false or invalid documents, etc hoping to slip through. If caught they will THEN try to argue they came for asylum, etc.

Or they attempt to enter claiming they are entering for another purpose (visit). Then when inside, if caught / challenged to leave, they then claim asylum.

The signs need to be seen in conjunction with the large detailed notices that appeared at the same time (in numerous languages) BEFORE you reach the now very clearly signed UK border control point, saying that if you wish to claim asylum, THIS is your time to do it, without committing any offence etc.
If you enter or attempt to enter without doing so NOW, and later are challenged, it may compromise your position with regard to illegal or attempted illegal entry, and may also harm your asylum claim.

It is similar nature of change to the change that happened to the wording of a standard police caution, which has changed form a simple right to remain silent to:
"You do not have to say anything, however it may harm your defence if you do not mention when questioned something that you later rely on in court."
- I.e. the failure to disclose something relevant early has, the potential, to be considered prejudicial. Which wasn't directly the case previously.