A one-time fee is a lot more palatable than an annual one.
Also, IMO the value of going from non-donor to Basic subscriber is much larger than going from Basic to Premium. However, the price points don’t reflect that.
"Thoughtful planning and preparation are key to a rewarding future, but we do not live in the future—we live in the present. It is day by day that we work out our plans for the future; it is day by day that we achieve our goals. It is one day at a time that we raise and nurture our families. It is one day at a time that we overcome imperfections. We endure in faith to the end one day at a time. It is the accumulation of many days well-lived that adds up to a full life and a saintly person."
- Elder D. Todd Christofferson