Adding my two cents to this topic, I haven't done any pairing for Chrom except Chrom x Sumia. Couldn't bring myself to experiment because both of them have less support options in terms of marriage. I also find that, while Inigo can benefit from Chrom, he can also gets many benefits from fathers like Virion (provides no overlapping classes and good mods) or Avatar (who is a good father/mother for anyone, depending on asset/flaw). I find that Cynthia gets more out of having Chrom as a father than Inigo, personally.
In short, nothing wrong with Chrom x Olivia, but the game really wants to shove Chrom x Sumia into your face by limiting them both in their options, so it makes perfect sense to pair them, and Inigo has better fathers than Chrom anyway.