Why were horse chestnuts and buckeyes moved from Hippocastanaceae into the soapberry family?

The classification of horse chestnuts and buckeyes (Aesculus) has been updated based on modern botanical research. While they were previously placed in their own family, Hippocastanaceae, they have been moved into the soapberry family (Sapindaceae) because scientific evidence has shown them to be temperate offshoots that evolved from within the largely tropical Sapindaceae lineage.1

This reclassification is supported by DNA sequence data, as well as analyses of morphological resemblances and chemical properties, which clarify the evolutionary relationships between the families within the order Sapindales. Similarly, the family Aceraceae (maples) was also integrated into Sapindaceae for the same evolutionary reasons.12