When you sign a receipt, you’re not just providing a sample of your signature for comparison against the one on the card. You are signing a document, usually saying that ‘I agree to comply with the terms of the cardholder agreement’
If this is no longer necessary, the card issuers must have determined that they have other legal agreements which cover purchases, and that the signature on each transaction is not necessary.
Also missing is a discussion of why PINs are not seen by the banks as an obvious next step.