Or at least, no changes significant enough to prevent them producing hybrid offspring.
There has still been significant evolution since they 'split' but there are still sufficient similarities to enable interbreeding and the production of infertile hybrids. This really isn't surprising.
If I'm not mistaken:
Creationists and Evolutionists would agree that the significant evolution that has produced the lions and tigers we have today, happened rapidly. From what I have read, there are various 'panthera' fossils which show a more punctuated evolution from the common ancestor than a gradual evolution.
Evolutionists say that short periods of rapid evolution were followed by hundreds of thousands of years of stasis (no evolutionary change); creationists say the changes occurred at some point during the last 6000 years.
The question for evolutionists is: realistically, what effect
would a million-odd years of post-'split' in-breeding have on the two species' ability to hybridize? Is it reasonable to believe that they could still hybridize after such a long time? Do we have any way of measuring this?
It seems that evolutionists see the geological record and
assume that such a great length of time has not affected their ability to hybridize, when actually there is no method by which we can predict the effect of this time, since we can only observe and measure changes that occur over hundreds of years.