Because that word is the best guess of modern scholarship about the original pronunciation of the name of God in ancient Judaism, which in English we can write as YHVH (Biblical Hebrew does not have vowels). Jews believe that YHVH is God's true name and it is extremely sacred to us. We believe that the true pronunciation has been lost and that we should never try to pronounce it.
It’s in the Bible too, when reading the Bible is it disrespectful to say it then? I can respect your refrain from pronouncing it. But, as someone who doesn’t practice that religion, being dissuaded from pronouncing the name feels like an attempt to keep people further away from god. Like in a relationship with someone, generally speaking if you care for them and trust them you’re going to call them by name.