Look how short the harpsichord keyboard is. This is becasue the user has to tune it each time it is used. Sort of like a guitar. And most users are incapable of "tempering" the tuning.
Wide keyboards, such as those on pianos must be tempered, or slightly detuned, or their lowest notes would sound out of tune with the highest notes. Tempering a piano is tricky and this is the reason there are professional piano tuners instead of tuning pegs on a piano.
The harpsichord, which must be tuned all the times, avoids the tempering requirement by keeping the keyboards short.