A lot of high volume investors spend a lot of money with GoDaddy and keeping money in the GoDaddy ecosystem can be perceived as beneficial for tax purposes[1] plus it minimises the burden of managing payments. I
suspect the bonus was a short term promotion to raise awareness of the "Good as Gold" program and their hope is that more people will use the program.
The bonus was a short term promotion that is over now.
Personally, I think the name is dumb, despite reading it often I don't associate it with being GoDaddy "account credit".
edit: oh!
The bonus is back, and more now. Definitely a compelling option, an extra 5% that I'll spend with GoDaddy anyway? Sure.
[1] Depending on the jurisdiction and the investor's appetite for risk and/or willingness to "accidentally" forget that these are taxable transactions anyway.