There are simply too many cars in the park now, far more than when I began visiting Whipsnade as an independent adult in the early 1980s.
To accommodate them, potential or actual exhibit space has been sacrificed (adjoining the elephant arena and in Bluebell Wood). Duke's Avenue in particular can be a minefield to cross with a small child or an elderly individual.
I think it has got to the point where only cars with small children (ie under 5), or genuine blue badge holders (ie physically impaired, either through age or disability) should be allowed into the park in high season. Increase the number of buses; children of all ages love using double-deckers!