Gilbertus Genebrard was 28 years old when he invented the Yahweh name. so far as we know he did not believe the name Jehovah was the true translation of the tetragrammaton. There were many who did not accept the name Jehovah. But they were not the bible makers. It was the bible makers who chose to put Jehovah in their translations. The Latin Vulgate (his bible) did not have the tetragrammaton. It did not have Jehovah. This was the Catholic bible from around 425AD (the Jerome translation) on up. He turned away from the Masoretic text to the Samaritan text to discover how these translated the tetragrammaton. It was believed that the Samaritan was the only surviving text that used the Paleo-Hebrew letters. When he obtained a copy he discovered the Samaritans had Yabe for the name of God. It was not translated from any tetragrammaton. Yabe is the same as Yave. He added the silent "h" and formed Yahve. Then adding the final silent "h" he had Yahveh. The "v" was chanted into a double "v or w" and the baby was born Yahweh.
Was he a member of some secret cult? We do not know yet. Was this the cause of his desire to prove Jehovah was false? We do not know. It is more likely he acted on his own and wanted to prove to the church of Rome it was wrong to accept the name Jehovah from the Masoretic text.
If I see anything, it could have been that he did not trust the Jews and their Masoretic Aramaic text. And since the name Jehovah was born from the Masoretic text he could not see how God would preserve his name among a Christ rejecting group of men. What ever his reason, he broke with the Masoretic text controlling his mind. He got rid of the trigger that deceived the world that the name of God was Jehovah. When he accepted the Samaritan Yabe, he was going totally away from the Jews to their enemies. While he was doing this, he had no idea that his new invention of Yahweh would be taken by William Gesenius and applied to the Aramaic language and vowel pointed to make it appear Yahweh came from the Jews and not the Samaritans.
There are many men who have studied this strange development of two totally different names of God and both taken from the tetragrammaton. But they never connected William Gesenius as the man who took a Samaritan name for God and turned it into a Jewish one.
A man God made