Use of "we have a large backlog" euphemism by journal editors when rejecting articles without sending them out for review Several times now I've had desk rejections from journals in pure mathematics that are variations on the theme of 'we have a large backlog of very good articles, so unfortunately we won't even be sending your paper to a referee even though we might ordinarily do so'. I suspect this is just euphemism for 'we aren't interested in your paper/your paper is not good enough/go away', as claiming a large backlog seems to me to be more objectively defendable than making an editorial decision (ie 'not significant enough') and standing by it on its own terms. Alternatively, it may be phrased this way to soften the blow in claiming to not make an explicit judgement call on paper quality.

Is this common practice among editors and/or journals? I haven't in my admittedly limited experience heard similar wording in rejections from, say, experimental sciences journals. More controversially, am I correct in my reading, that it is just euphemism? (If so, I do not appreciate it, in the interest of academic honesty over lawyer-approved weasel words.)

Ideally answers would come from people who are editors and/or those with extensive experience in publishing. A bonus would be answers that can detail whether this sort of thing is on the rise, coming from people who have decades of experience.
Although I've not been "an editor", I've been involved-enough with refereeing in "pure math" for almost 40 years now that I can observe some patterns:

First, the last several decades were very productive in the sense that many, many people got PhD's in math from pretty darn good places, and were focused on research. Second, the advent of TeX + internet (as opposed to paper mail) has effectively decreased the "friction" of submission so that the volume of submissions is insanely higher than 30 years ago. Maybe 100 times that rate? Meanwhile, the number of reasonably-substantive-status mathematics journals has not at all increased, and the refereeing system (pro bono, in people's spare time) has not changed. I hesitate to suggest that referees should be paid (jeez, for one thing, this starts to create conflicts of interest worse than those already present...), but the "old" system cannot cope with the new volume.

Thus, desk rejections will be more frequent, and more aggressive. That is, in particular, editors will not want to annoy/burden their "stable" of expert referees with a higher volume of papers... (One could hope that the pool of expert referees would grow proportionately to the number of TeX'd-up manuscripts, but this seems not to be so.)

Yes, I'd be willing to believe that the rate of inaccurate desk-rejections has gone up... not through malice or prejudice, but exigency.