why do companies make the same car with different badging??

[84LX89GT]

If you were a company that pinches pennies in every area possible, why not rebadge cars that you or other people build? It cuts down on cost, and gives more people options of styles (even though very similar) and it saves a TON of money on tooling and car research and devolopment. Although some cars are rediculously similar to each other (like early 80's GM products....pontiac, chevy and buick cars were almost identical in everyway except for slight badging differences). this also applies to the fox bodies of the 80's except alot were pretty different although all boxy.
If i was a car company i'd probably do the same thing. If people buy the mercury or lincoln vehicles based very closely on ford's why not build them that way. It cuts down on vehicle cost as well for the customer for initial purchase and parts cost.