It's a poor attraction and tourists only visit it if they have no other choice.

In general, both tourists and Tropicans prefer to visit buildings that have a high service quality, and most of the buildings that you're likely to build as tourist attractions have much higher base and maximum service qualities than Scenic Overlooks and Souvenir Shops. If there's enough buildings with higher service quality available, then tourists will go to them instead of to your Scenic Overlooks and Souvenir Shops.

Souvenir Shops might be worth building in the center of a cluster of three or four wonders since if I recall correctly they gain 10 points of efficiency (5.5 service quality) per nearby wonder.

As the others mentions, tourists will pick the entertainment building with the highest rating, that they can afford, and has free space.

As the Souvenir Shop has low Service Rating, it will usually be the last thing they pick. But that has its uses: If you see tourists actually visiting the Souvenir Shop, then you are running out of other, higher quality entertainment that gives more profit.

The Scenic Outlook can serve the same purpose, and requires no employees.