Complex sentence: Despite their close friendship, there is no record that Pitt offered Wilberforce a ministerial position in this or future governments, perhaps due to Wilberforce's wish to remain an independent MP.
Split into simpler sentences: Despite their close friendship, there is no record that Pitt offered Wilberforce a ministerial position in this or future governments. This may have been due to Wilberforce's wish to remain an independent MP.