Phred, although I have not yet reentered the world of international travel and researching and purchasing tickets since the start of the pandemic, prior to March 2020 I always tracked fares for many years via Google, and this pattern is exactly what I found pre pandemic when buying tickets for flights to Europe, crazy day to day moves up and down 6 months or more out from travel dates I was investigating, daily swings of 20 percent or more, back and forth. I only point this out as a way to say it is the "same as it ever was" because many people seem to think this craziness only started in recent years - in my experience, it has been like this for at least the last decade.
Also, several cite how Delta has recently priced itself out of their plans, and I agree with that completely, but it is not just in the recent past I have found this to be true. When it comes to actual dates and the need to pull the trigger on ticket purchases in the past, Delta was and still is consistently the most expensive fare, and as a result I mostly have flown American and occasionally United to Europe, but especially internationally I haven't flown on Delta in at least 10 years, and in a lifetime of flying to Europe mostly on my own dime, Delta has always been the least competitive option for me (and for most of my life I have lived in "Delta country" in the south and southeastern part of the US).
Delta has always been the least competitive price in my experience, to the point now that I seldom even bother with pricing flights on Delta. Back in the day when I flew on someone else's nickel, I flew Delta, but when it came to me using my own money for personal travel, American and United compete for my money on international routes, and domestically I also use Southwest and Jet Blue fairly often, too, but never Delta...