PIP is to cover the extra care & mobility costs arising from being disabled. It has nothing to do with employment status.

ESA is an income replacement for people unable to work due to illness.

Being different benefits with different purposes, they have very different eligibility criteria. Merging assessments would cause huge harm, especially for PIP claimants in work or planning to move into work.

UC should be a lesson about merging unrelated benefits.

Rudd's speech https://www.gov.uk/government/speeches/closing-the-gap-between-intention-and-experience?utm_source=dwppressoffice&utm_medium=twitter&utm_term=&utm_content=&utm_campaign=