For some terrain generation values, swamps occasionally generate surrounded by deserts. This seems out of place, as one would expect some other terrain to generate here. I think the terrain should be something else that's dry and flat (high Temperature, high Erosion).
Sample affected values from seed 5116735402577285868:
x:-17232 z:-5736 (swamp) C0.402 E0.660 T0.742 H-0.026 W0.240 | (nearby desert) C0.276 E0.672 T0.757 H-0.150 W0.403
x:-13348 z:8104 (swamp) C0.219 E0.623 T0.753 H0.021 W1.157 | (nearby desert) C0.214 E0.627 T0.752 H-0.012 W0.894
x:5288 z:7832 (swamp) C0.149 E0.746 T0.640 H0.328 W0.272 | (nearby desert) C0.274 E0.840 T0.606 H0.234 W-0.392
x:-13856 z:520 (swamp) C0.057 E0.623 T0.578 H0.296 W0.032 | (nearby desert) C0.113 E0.591 T0.588 H0.241 W-0.436
All these have a high E (erosion) value around 0.7, and a high T (temperature) value around 0.6.
Related issue: MC-237621.
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Screenshot https://bugs.mojang.com/secure/attachment/456185/2021-11-09_22.43.45.png taken near -13348,8104 for seed 5116735402577285868. Elevated terrain surrounds the swamp on all sides. This elevated terrain suggests that the swamp should have generated as a different, elevated biome. Stony peaks is a likely candidate here.
Actually, the E value stands for erosion, which controls how flat the terrain is, which means that mountainous biomes like the stony peaks generate when erosion is low, while swamps only generate when erosion is very high, so that they can always be near sea level. Also, deserts are more likely generate in areas with high erosion, and can't generate near mountains, as these get replaced by badlands instead of stony peaks.
I accept Gabriel's corrections. I have since checked the values for actual stony peaks and I have found the values (particularly the "E" value) to be different to what I expected (it was negative).
I have found that badlands generate frequently with deserts (they are shown in the biome map as a darker orange) but stony peaks with deserts are quite rare. This is why I guessed that the swamps should have been stony peaks.
Some biomes in the terrain generation arrays are known to occur more than once (see MC-237621), so it's not unreasonable to suppose that whatever replaces these swamps would also occur multiple times.
I suspect this is Working as Intended, with a possible future change of these swamps to some kind of oasis biome.
Attached is a biome map that shows what is going on for seed 5116735402577285868. The four areas of interest are marked with a white box, see description for coordinates. Swamps are cyan, deserts are orange. The biome colours are similar to the Amidst software.
Others have remarked elsewhere that stony peaks seem to be rare. My testing has confirmed this (less than 0.1%). This bug report could be why.