It may sound crazy but vehicle paintwork is very delicate and can easily be damaged by the sun, bird droppings, acid rain and just everyday wear and tear!
Today there are a massive range of paint protection options from waxes, sealants to ceramic coatings. some of these options come with some very hefty price tags too.
Personally in my experience , the depth of shine is all in the preparation, if the surface is correctly cleaned and decontaminated then a top quality wax or sealant is applied then this is perfectly good for 99% of car owners and will give a superb shine.
If you are looking for mirror finishes then machine polishing is the way to go, But this is slow going and usually needs a full day at the very least to get the desired results.
Paint restoration (see image for a 50/50 of before and after) the paint was severely sun damaged after machine polishing the desired result was achieved. unfortunately when doing work like this the paint is thinned down a little and it can only be done a few times maximum.
Please call me for advice and to discuss your requirements.