I think the relatively recent trend of "deer sniping" has contributed to a lot of the horsepower one sees at the "deer rifle sight in day" events lately.
I suppose "relatively recent" is non-descript, so this might be referring to "relatively recent compared to the age of the world," but watching the history of magnum cartridge and US hunters, it's not really recent, and the recent trend is towards smaller and smaller cartridges, not larger and larger.
Consider when most magnum cartridges were designed - we're talking 50-70yrs ago. The 300 Wby magnum existed pre- WWII, with the 30-378 coming out in the late 50's, and the 300 wm and 7 RM on its heels, originating in the 1960's out of the post-war American principle of "bigger is better". There was a relative stagnation where the interest here hit a carrying capacity of "special interest" folks for a couple of decades, but when the Remington Ultra Magnums dropped in 1999, almost 25yrs ago, surrounded by fanfare of "shooting across canyons" there was a huge boom in magnumitis.
BUT... Almost immediately thereafter, we saw the introduction of the WSM's and RSAUM's, and the "down trend" of case sizes began. The WSM's hit the market in 2001, with the WSSM's in 2003 behind them, and the Ruger Safari Magnums came out in 2007, smaller than the cases of their much older counterparts. It really wasn't until the 300 PRC hit the market that we had a truly larger capacity magnum come to market as a factory offering, larger than its long-standing counterpart, but still not larger than many of its competition in the large 30 cal magnum class.
But comparatively, we're seeing much more being done with relatively SMALLER cases, even within the magnum cartridge category - the 6.5 PRC is smaller than either the 6.5 Rem Mag or 264 Win Mag; the 7 PRC isn't bigger than 7RM or 7RUM, 300 PRC is slightly bigger than 300WM, but smaller than RUM, Norma, or either 30 cal Weatherby. 6.5 and 6 Creed smaller than the 260 rem and 243win, 6.5 Grendel smaller than 260rem, and 6 ARC even smaller still than the Grendel. I suppose 224 Valkyrie and 22 Nosler were larger cases than 223/5.56, but remaining smaller than 22-250 or 220 Swift, and smaller cases than their 6.8 SPC parent... We're seeing more and more SMALLER cases being developed and released - which is largely being attributed to 1) the death of hunting in the US, 2) more efficient case designs getting more performance out of less powder, and 3) improved bullet technology.
More often, at the ranges I frequent, I'm seeing more and more SMALLER cases in the last 10yrs old than I did in the 20yrs before, and when someone brings a magnum cartridge to the line, it's typically someone heading out of state after larger game, or an older hunter with a rifle bought a generation ago, or two...