Let us think from end user standpoint.See less
Uber cab app - the intent of the app is to travel. This means the location of the users would change. Most uber users book cab for themselves - (this is evident from their existing product flow)
Uber eats app - the intent is to order food at home. This means the user will be at a fixed location at that point of time. Most of the uber eats deliveries are not scheduled for future delivery time.
So, fundamentaly, the user intent of the app is different. Hence cant be merged.
Other reasons are mentioned above.