Mostly to get attention. There are maid restaurants, but the girls working there will only wear the dress inside. The girls wearing stuff like that outside are most likely doing cosplay. Which means to dress up as someone and maybe have strangers take pictures of you.

girls might WORK in theme restaurants , if her face is older looking, but in Harajuku, Tokyo, dressing up and visiting Harajuku, Tokyo from hours away is a big deal on weekends for teenage girls.

Harajuku, Tokyo, especially near Jingu Bridge, especially on a Sunday

A Beginner’s Guide to Harajuku’s Lolita Fashion:

https://savvytokyo.com/a-beginners-guide-to-harajukus-lolita-fashion/

Cosplayers are people who dress up as anime, manga and cartoon characters, in specific dresses or as members of popular bands. Lolita fashion is also popular in Harajuku, ranging from a wide range of genres including gothic lolita, fairy lolita, punk lolita, and the classic lolita

from https://jpninfo.com/5912