Because GM dumped Lotus due to the recession in the early '90's. GM commissioned Lotus in the mid '80's to develop an entry level sports car that would cost in the mid 20's, and put enormous resources and money into the Elan project. Unfortunately cost overruns (the Elan interior and convertible roof design alone cost more than entire previous Lotus production lines)and delays killed the Elan.
Lotus was in dire straights and needed to produce a car that was relatively inexpensive to make. The S1 Elise cost a fraction per unit, compared to the Elan,in part to its relatively simple design plus the fact that it was not intended for the US market, saving Lotus the costs of federalization ($$$). Thus the Elise "saved" Lotus.
There were rumors of future developments for the Elan, including an AWD version; what might have been.
Had the Elan come out years sooner with its initial target price in the mid 20's as opposed to the final price in the 40k price range, the story might have been different. Nobody was going to pay that kind of cash for a fwd car (rightfully so).
Look at a lot of the rwd performance cars today; they are saddled with all sorts of safety features to keep the driver from getting in to too much trouble. The Elan had none of those (not even abs). The Elise was only allowed in the US by way of financial hardship waivers granted by the DOT. Whether this will save the Lotus over here, we shall see.
As an aside, GM has always experimented with fwd cars that in no way could be construed as econoboxes. The '60's Toronado comes to mind
. Not suprising that GM also owns Saab, a carmaker that has been committed to fwd since its inception.