It was a doxology added in where it did not belong.
Likewise the divide between the science of textual criticism and doctrine of Biblical preservation.
The omission of the phrase from the Chester Beatty papyri is the reason the NIV and other modern translations omit it today. And yet, P46 is known to be riddled with transcription errors. The task of copying on papyrus was notoriously difficult and, in my view, the weight given to papyrus fragments in translations should take that into account as well. IOW, when it comes to papyri, the more the better.
Bottom line, the majority text (consensus) and Textus Receptus are very close indeed. So even when the critical text (as with Matthew 6:13) does not agree - the words of God are preserved. Not by man, by God.
To God be the glory!