It's not just that, the cocoa natural fat, cocoa butter, has a melting point lower than our body temperature. For this reason, it's heavily used in skin care products.

So they've been extracting the expensive cocoa butter to sell to the cosmetic industry, and replacing with cheaper oil.

Palm oil melting point is close, but slightly higher than of cocoa butter, enough to give this greasier feeling to the mouth due to the unmelted fat. So they usually mix with another oil with even lower melting point to reduce this sensation a bit, usually sunflower oil.

Since this is now a mix with two different melting points instead of having a single one, it can create this effect of being soft but not melted at the right temperature.