I don't think that's the main reason returns were sent too early. W-2s and 1099's did not have to be mailed until February 1, and the mail is still arriving. Many practitioners can't collect their fees until they tell clients that the return has been filed. IRS is doing all it can to discourage people from staying in the business, by squeezing the filing season down to the gestation period of a poodle.
If a person walks into your office on January 15th with five W-2s I will bet you 10 pounds of lutefisk that there will be a 6th or 7th arriving shortly after that return is filed. Everybody is hot to trot to get their refund and most preparers are hot to trot to get that return prepared and filed so they can collect their big bucks for their preparation work. Should I throw in the additional fact that a lot of preparers using Intuit software aren't exactly rocket scientists?
ACME trench digging shovels on sale this month
I'm old enough to remember when W-2s were issued as soon as the books were closed. The little man with the green eyeshade prided himself on finishing them early. It's only when the big payroll companies took over that they decided January 31 was not the last day, it was the only day they could send them out. That way they avoided sending duplicates to folks who lost the original before they were ready to file.