This site says:
Plants hybridize much more frequently and successfully than animals do. [...] Chromosomal doubling (polyploidy) occurs more frequently in plants and facilitates the fertility of the hybrid offspring.
Outcomes of the successful hybridization of different species of plants (i.e. yelding fertile offspring) can be easily observed in agriculture - for instance, Triticum aestivum is 6n, while Triticum durum is 4n. The latter comes from the hybridization of two plants from different genera (!). So it seems to me that not only can plants hybridize more easily, but also that the evolutionary distance between the parents can be greater than in animals.
As far as I know, the preferred animal strategy to have fertile hybrids is to go partheno/androgenic (for example in Phasmida).
My question is:
Why can plants produce fertile hybrids more often than animals? What constraints are present in animals and absent in plants?
To my knowledge, polyploidization is the main mechanism by which this is achieved. If this is true, then my previous question can be rephrased as why does animal polyploidization occur more rarely?
I'm not entirely sure about my assumptions, so feel free to correct me, of course with references.