Why is Pluto's orbit so stretched and tilted compared with the planets' orbits?

Answer: Neptune's gravity pushed it outward and locked its orbit

It's too far away for the Sun's gravity to keep it circular — Distance doesn't force an orbit into an oval; Neptune, also far out, moves on a nearly circular path. An orbit's shape depends on the object's history, and Pluto's was shaped by Neptune.

Neptune's gravity pushed it outward and locked its orbit ✓ — As Neptune slowly migrated outward early in the solar system, its gravity herded Pluto into a stretched, tilted path. Pluto now circles the Sun exactly twice for every three Neptune orbits, a lock that keeps the two apart even though their paths cross.

The solar wind has slowly pushed it off course — The solar wind is far too thin to push a world like Pluto off course. Pluto's unusual orbit was set by Neptune's gravity billions of years ago.