Why don't naval ships have multi-scale digital camouflage for their paint job to blend in with the ocean?

They do, at least did, in WWII. The British called it “dazzle” while the US called it “razzle dazzle.”
In peace time, you want other nations to see your ships. In war time, you want to confuse enemy subs.

I am just speculating, but I think it has to do with the fact that modern ship weapons operate at far longer ranges than the main battleship guns of yore, where visual targetting by a fleshbag, which the camo pattern is intended for, is no longer a factor. I doubt that camouflage patterns are at all effective against radar or laser targetting.
As for missiles, which I believe is now the main form of weapon used, they seem to have switched from the strategy of “avoid getting hit”, to “shoot down the missile”.

Probably because camouflage doesn’t do anything to conceal the wake behind the ship or keep it from showing up against the horizon. Nor does it block out radar or sonar. And it cannot block the sound of the engines and propellers from reaching those looking for it.

I’m pretty sure some of the smaller crafts still use camouflage paint.

We don’t use camouflage on big ships and submarines anymore, but they are still grey I think, which at night blends in, it’s not like we paint them red or bright white. I don’t know if they worry about their big ships blending into the background or not. I agree that with radar and sonar, it’s hard to hide now.

So many great answers. I feel kind of stupid for even asking the question because they’re all so self-evident (especially the wake). Thanks!

This is a twisting story, but be patient.
Yehudi Menuhin’s parents rented an apartment. The landlord then told them “You’ll be glad to know we don’t rent to Jews!”. They then told him they were, and found another place to live. They named their son Yehudi, which means “The Jew”.
He became a famous violinist; a child prodigy. When he was to appear on the Bob Hope radio show. During his introduction by Hope, singer/comedian Jerry Colonna drew howls of laughter by interrupting with “Who’s Yahooti?”. That became a famous catchphrase, even inspiring a popular song.
During World War II, German U-boats were a terror on the seas. These submarines would see American aircraft miles away, and would dive to avoid being bombed. The Americans developed lights to shine on the planes, to match the sky illumination, which worked as camouflage. The planes were suddenly nearly invisible until they were half a mile away, not giving the U-boats time to submerge. These were then called Yehudi Lights.
Despite this development, they were never used in the war. Why? Radar had been created and deployed.
So, there’s your answer, at last. Radar.

At the end of WWII, even with the advent of radar, the US NAVY employed razzle dazzle. You can find pictures of the USS North Carolina, sunk at Pearl Harbor, raised, repaired, refurbished and used at Normandy on D-Day, 1944,, in full razzle dazzle paint.
Other ships with the paint scheme in 1944 were the USS Missouri, and aircraft carriers in the Pacific, to name a few.

@kritiper I’d never seen” Razzle Dazzle” before. WOW. Thanks for the education. I do wonder if we might one day see a return to this kind of thing (perhaps with mirrors or lasers/lights) to mess with AI image recognition. We’ve seen the Ukraine kamikaze drone boats in action, and I think threats of that nature are only going to become more ubiquitous and advanced in the years to come.