Yes they probably lobby against it, so would any company if its important to them. $5 mil in lobbying is loose change. These are not big businesses - HR Block has a market cap of $4 Billion about the same as a bunch of companies no one has heard of.
However the real reason is politicians making the tax code as complicated as possible, giving breaks to favored groups.
You can't believe such a hugely important thing as tax is swayed by such a little piece of lobbying.