It's a mistake for non immerito, which indeed means "not without cause." The phrase is classical and abundantly attested.

In your second link, it can be difficult to see, but it's actually an 'e' and not an 'o' at the end of the line there. If you look e.g. at this transcription, you get non immerito plenty of times and non immorito a couple, but if you check in the actual text where immorito occurs, you can see even more clearly than your examples that it's just an OCR mistake and the word is actually immerito.

It's a mistake for non immerito, which indeed means "not without cause." The phrase is classical and abundantly attested.

In your second link, it can be difficult to see, but it's actually an 'e' and not an 'o' at the end of the line there. If you look e.g. at this transcription, you get non immerito plenty of times and non immorito a couple, but if you check in the actual text where immorito occurs, you can see even more clearly than your examples that it's just an OCR mistake and the word is actually immerito.

Edit: Looked again, and even on that first link, you can see there's a difference between the second vowel and the fourth vowel. It's immerito, not immorito.