Actually they always gave credit when due.
Out of some 90 they recorded, they've been in trouble for, a grand total of - 3 songs. My my that's a mightily high number of songs, a "bunch".
Out of those three, one of which was unknowingly and they settled it by giving credit without any issues. The other was also settled in court. And the last one(weak case)they won in court.
So that's just one song that they had to be forced to give credit through legal proceedings( The Beatles had just as many).
You sound like one of those imbeciles easily swayed by lies and rumours so next time actually try researching and formulating an independent opinion than being a sheep.