Why are some angels considered as "saints"?

It doesn't matter for a Saint to be named or canonized thru Catholic Christian traditions. As long as a being have done a holy supreme sacrifice services for others and for self to glorify God . Just like Mother Theresa was already been a living saint. There a lots and so many or a million of unnamed Saints in the Bible from Old Testaments to New Testaments including unborn children. Until now or today presently there a lots of Saints doing their services. Martyrs and untitled or unknown heroes. For angles or archangels, yep, they consider Saints also. Though, they don't have freewill just like us humans created by God. That's why an angel name Satan rebelled God because God gave humans the divine gift of freewill or the freedom to choose including to create. For other angels or archangels, their wills are always and forever of services or servants accordingly to the will of God and to all of us humans.

There are no angels... they are just a myth and fabrication of human imagination. All religions have saints who’re of holy and religious disposition and who guide the general people about God, religion and the correct path to know God.

The saint tag put on the angels was done by the catholics. They are not saints. Saints were invented by catholics anyway.

Angel is a figment of human imagination. Its origin can be traced to Bible. Angel Gabriel had appeared to Mary to announce that she would conceive and bear a Son. God would be its father. Catholics propounded the theory of Angels further. They call persons of exceptional holiness as angels.