How do you think simplicity of "A Red, Red Rose" appeals to Burns's readers?

The red rose has long been a symbol of love. On Valentine's Day, it's customary for men to send a dozen red roses to their wives or girlfriends. In Burns's day, too, the red rose was associated with romantic love in the popular imagination. Burns wanted this poem, as with all his works, to have the widest possible audience. He wanted his poetry to be read not only by a small literary elite, but by the ordinary people, the common folk, those of a similar background to Burns himself. So in writing "A Red, Red Rose," Burns deliberately uses a symbol to which just about everyone can relate. There's no attempt here at complex symbolism; Burns wants to keep things as simple as possible without sacrificing lyrical intensity.
One should also bear in mind that, though much anthologized as a poem, the piece was originally written as a song. Burns deliberately set out to write a popular song that would be loudly sung by common folk the length and breadth of his native Scotland. And what better way to achieve popular success for a love song than by the use of a symbol that everyone can immediately understand?
https://www.poetryfoundation.org/poems/43812/a-red-red-rose