He told the others how to conjure the three flowers out of a genuine sense of philanthropy towards them. His ancestor risked his life to defend this place, after all.
He had given them several ways that they could conjure the three flowers. Despite the others having their own methods to do so, most of them needed to be used together with their own cultivation methods to work.
As such, he then gave them several ways which were more ubiquitous among the worlds, mainly methods which the lone cultivators used.
If the Immemorial Path could find ways suitable for their own use from such foundations, they would then be truly on the right path.
Having gained such a massive boon, those of the Holy Sun Continent wouldn't just let Lu Xuan do so for free. As a result, they then gave him some kind of immense treasure.