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Fertility levels for the hybrid animals (ligers, tigons, etc.) are far too low for replacement levels in the wild even if they did occur there. Not to mention they show a number of behavioral confusions reflecting the differences in how lions and tigers behave out there. An interesting genetic difference can lead to gigantism in ligers and runtiness in tigons. That is, at least one important growth hormone's gene is on the X chromosome in one species and the Y in the other.

They're speciated from each other, just not too long ago. If all we had were fossil skeletons, we'd have no clue that it had happened at all, BTW.

We have examples of even more recent and less complete speciation, such as rings species in birds and salamanders. Horses and donkeys are an example of a more complete speciation. (Mules and hinnys are almost always sterile.)

In fact, we have almost any degree of speciation and not-quite speciation one might expect if evolution were producing the diversity of life. What we don't see are any easy, natural groupings of created kinds unrelated to each other.