The reasons why so many musicians mention these albums? Firstly, that Joni Mitchell’s Blue used many unique guitar tunings and sounds while also being such a highly emotional and autobiographical album. It communicated in a highly sophisticated, musical and lyrical way her breakup from Graham Nash (Hollies and Crosby, Stills & Nash) with both the music and lyrics working as one to create a very personal yet relatable album that is a complete musical work of art.
With The Rolling Stones Exile on Main Street is seen by musicians as covering so many genres of music and incorporating their free spirit approach to making music while acting as the pinnacle of all their earlier albums. Basically it’s now regarded by many musicians as their most musically important hard rock album.
Does this mean that Blue and Exile on Main Street are their best albums? From some aspects yes, but from the general public’s perspective not necessarily so.