Why is my tiger not sharp?

Just back from a safari in India. I will post some representative shots soon, but wanted to separately ask for advice on some unsharp tiger shots. Here's an example:

Fine at small sized, but not fine when enlarged. I'd be afraid to print at the sizes we usually do (e.g., 16 x 20). EXIF is embedded, but this is 1/250 sec., 75-300 lens at 300 mm. I am just used to better than this with similar settings and situations. It's on a monopod (tripod too awkward for the jeeps) with IBIS on. As I say, I've done a LOT like this and most seem much sharper. Despite the possibility of motion blur (from people moving in the jeep!), I got too many vaguely unsharp ones like this compared to prior experiences. Yeah, ISO 640 here, but that's really not bad and a bunch of other similarly unsharp pix were lower ISO.

Doesn't look like missed focus. (The leaves in front or behind the tiger don't seem to show sharpness away from the tiger.) Depth of field is something between 5 feet (estimating the tiger at 60 ft.) to 7 feet (if the tiger is more like 100 feet). So mis-focus seems less likely, a priori. No double images (shutter shock?) or directional smear that I can detect. And why would the cam miss-focus on this scene anyway?

For comparison, this is a more typical shot under basically the same conditions, EXCEPT that it should be LESS sharp owing to the 2x digital tele conversion.

So, what's up? I can find similarly modestly unsharp photos, and other sharper ones under the same conditions, if that'd help.