One of the more practical reasons is that particles from the Holy Host fall to the ground, when it is manipulated by more then one hand. And we know that no matter how small a crumb may be, it is still Christ. Hence when you receive Holy Communion in the hand some crumbs remain on your hand, which you dismiss as being nothing, when actually it’s everything. This falls to the ground and gets trampled by the legion of believers, who walk over Christ.
On a spiritual dimension. In sorts, it empowers you over God. Even if you don’t realize it. Holding God in the hand, you may be tempted to say: I got you!
God raised Jesus, so that at the name of Jesus every knee should bow, in heaven and on earth and under the earth, (Phil 2,10) The proper body position in front of God Almighty is kneeling, and not standing. Standing is the position between equals. We are not equal to God. But modernity has gone even further. Man is above God.
On an historical level, this practice was never present in the 2000 years of the Church. There has been receiving in the hand communion in the first centuries, but it was totally different from what we have today. You we’re required to kneel, even if you received in the hand. Then you we’re not supposed to touch the sacred Host, but to eat it out of your palm, and thus cleaning it in the process of every potential particle that may remain. And for women was required that they had a white veil over the hand that they received, which was later cleaned in water, and the water thrown over flowers.
As you can see, even receiving in the hand required quite a bit of reverence, if not more reverence then on the tongue. But only if done properly. God bless!