The reason, as anyone who has read and followed more than a few "Materials and Methods" sections can tell you, is that this style of writing makes it very easy to skim through and find the relevant bits. The last thing you want to have to do with a pipette in hand is wade through someone's flowery prose to find out how many microliters to dispense.
Perhaps it varies with the field.
"Here we make use of measurable selection."
So, use of the first person, plural is quite widely accepted in nearly all of current and recent mathematics.
I wrote my Ph.D. dissertation this way, and one professor said "When you say 'we' maybe I don't agree?" and thankfully a fellow student spoke right up and defended me; she explained that using "we" was standard in mathematics.
Once I was trying to socialize with a high school English teacher and sent her a draft of a paper I was about to publish in some applied mathematics and asked her to give the paper a critical reading. Soon she asked me if using "we" was standard in mathematics, and I had to say yes. She gave me no more feedback! Gee, that's much better than what I got from English teachers in high school and college!
In the end, I first learned to write in college and by writing proofs in pure mathematics; the reason I was able to soak up the lessons was that such writing, as English, is so darned simple. Later I branched out from such simplistic writing.
Later I was trying to socialize with a woman who was a secretary in a university. She confessed that, in her experience typing, etc., the really clear writing was from the professors of mathematics and the physical sciences. Maybe she was just trying to butter me up!
I disagree that 1st person voice results in flowery prose. Bad writing remains bad independent of passive or first person style.
It can be much clearer and, well, direct to use first person voice ("To assess wether the effect data X suggests holds true when Y, we do Z1, Z2, and Z3 as they cover Y1, Y2, Y3". This is clean and clear and much nicer than the respective passive voice. But again, perhaps just my opinion.
Gee, in high school I was taught that a preposition is a bad word to end a sentence with!
Also, a need for references. Not just citations, but verbal references. What is jargon, after all, if not a specific and functional set of keywords and referents used in common by a given group or field? Jargon is efficient in academia. It is a common standard. If I write something in my field's jargon, people in that field will know what I'm talking about, and precisely what I'm talking about. This is more efficient, sadly, than trying to turn a clever phrase to describe a phenomenon there's already a perfectly dreadful word for.