Because that, "when they knew God", they glorified him not "as" God, neither were "thankful"; but became vain in their imaginations, and their foolish heart was darkened. Romans 1:21
About me in a great land I see many now living by their vain imaginations and from a foolish heart that has no light of life within.
And changed the glory of the uncorruptible God into an image made like to corruptible man, and to birds, and fourfooted beasts, and creeping things. Romans 1:23
Striving for their own paths, grabbing all the material gain of Babylon. Their uncleanness now shows forth, for they refuse to worship Him but rather the creatures.
Wherefore God also "gave them up" to uncleanness through the lusts of their own hearts, to dishonour their own bodies between themselves: Romans 1:24
God had no choice but to "gave them up" and they now show the results of their hearts, a flame burning by desires of evil; seen by actions of homosexuality and lesbianism.
Mocking the image of God which man was created in.
For this cause God gave them up unto vile affections: for even their women did change the natural use into that which is against nature:
And likewise also the men, leaving the natural use of the woman, burned in their lust one toward another; men with men working that which is unseemly, and receiving in themselves that recompence of their error which was meet. Romans 1:26,27