Making the game working online (which is where their money truly is) is probably much harder and they do not want to spend their best developers integrating GTA in Switch network. GTA trilogy was just ports of single player games, so they released on Switch, minimum effort required
GTA V being released on PS5 and Series XS is much more a matter of keep the current installbase buzzy when they upgrade their hardware, instead of letting them play another thing when waiting for GTA VI
This is almost certainly correct. Their bread is buttered by GTA Online. The Switch really isn't setup for that.
In any case, Take Two is a big company. The decision not to port it to Switch was made purely by the numbers. So, something tells them that the ROI isn't there.