Top of Mind... Why do dominate brands continue to advertise?
It is really quite simple. Our brains have limits and functionally work a bit like a waste basket. When met with a question our brain seeks out the answer accessing the most recently deposited information first. It has also been established that categorically our brains only maintain a small number of options most experts believe 4 items is the relative max at this point in time (down from 7 back in the 60's).
Why this matters, let's say you're an attorney, an attorney that is interested in keeping existing and building new business. You are no doubt counting on the great previous work you have done to bring referral business. I am here to be very clear that referral base is at risk even if they loved your work. The evidence is clear if your former client is not consistently reminded that you exist, another 4 attorneys can market to or become more recently important (help their sister with a case), and you will fall out of their memory bank.
Make certain your marketing strategy is working the entire sales funnel to include retention of existing clients, your success may well depend on it. Just look at "Tide" as a product, the domination, and apparent loyalty that Tide has might make you believe it's invulnerable, but Proctor and Gamble know without a doubt it is the unrelenting volume of advertisements that keep it Top Of Mind.