I think that you don't want your landing pages to look too basic or that can make them look like a low quality website and then people might not put any trust in what you are trying to offer your visitors.
A lot of landing pages look kind of basic because many are scripts that were either made for the uses of the masses, were not intended to be elaborate because that takes time if you build it yourself, are PLR templates or came with some kind of money making program/package.
Most marketers don't want to spend time creating elaborate landing pages or pay someone to have them created.
I think that how your landing pages will also depend on the niche that you are in for that landing page. Since I am mainly in the fashion niche it is better to have some real nice but I think that some niches will work fine with something basic and not real fancy.
Users mostly prefer to use simple and clean website and they always abandon website with a complex User Interface. But properly designed landing pages increase the conversion rate. It is always advice able to keep advertisements to minimum. Majority of the website display too many advertisements at the landing pages and as a result they end up redirecting traffic to other users. Even using good color schemes and HD images at the landing page can attract the audience.
The landing pages that you are referring might be just for getting the subscribers get into the funnel. It also depends on the objective of the person. Most of the time having a good landing page is not enough, your CTA's also matter along with the message.