From Not Exactly Rocket Science:

In the Old English of Beowulf, seven different rules competed for governance of English verbs, and only about 75% followed the “-ed” rule. As the centuries ticked by, the irregular verbs became fewer and far between. With new additions to the lexicon taking on the standard regular form (‘googled’ and ’emailed’), the irregulars face massive pressure to regularise and conform.

Today, less than 3% of verbs are irregular but they wield a disproportionate power. The ten most commonly used English verbs – be, have, do, go say, can, will, see, take and get – are all irregular. Lieberman found that this is because irregular verbs are weeded out much more slowly if they are commonly used.

To get by, speakers have to use common verbs correctly. More obscure irregular verbs, however, are less readily learned and more easily forgotten, and their misuse is less frequently corrected. That creates a situation where ‘mutant’ versions that obey the regular “-ed” rule can creep in and start taking over.