Imputed notice exists owing to the reality and practical considerations of title purchasing.
In reality, it is often not the purchaser themselves who will make full inspections, whether legal or physical, of the title to find evidence of legal or equitable interests.
This is a job usually left to representatives of the purchaser such a a solicitor.
Imputed notice means that if a representative of the purchaser has been given actual or constrictive notice, this is also bound on the purchaser themselves.