Not the sole reason. They play a part, same with H&R Block, but it's more the people working for the ultra-wealthy who keep bribing politicians to create laws that allow their clients to avoid paying taxes. The companies that have tax software for the small people benefit from the tax system getting more complex, but they don't directly lobby for those rules, they just want any kind of complexity. Their big fight is against any kind of free tax preparation for the poor and middle class.

It's pretty disgusting what they do though. They make say $20 from someone filing their taxes. They take say $3 from that $20 and spend it to ensure that their customers are never offered a free alternative. They're basically making their customers pay to lobby the government to keep taxes so complex that the customer has no choice but to use them again next year.