TVs can be fitted to TV wall mounts by a kind of 'hole pattern' (known as a VESA pattern) on the back of the TV. The back of most OLED televisions are different to those of regular TVs:
the dimensions of the 'hole patterns' are often a maximum of 400 mm wide x 200 mm high (VESA 400 x 200) and the 'hole patterns' are usually positioned at the bottom of the TV.
The OLED TV wall mount is designed to be a fit for this special pattern, for example with the shortened mounting pieces.