It shows a lack of attention to detail, a lack of viewing the full picture of all your potential users, and a lack of consideration for those with accessibility

It shows a lack of attention to detail, a lack of viewing the full picture of all your potential users, and a lack of consideration for those with accessibility issues. Therefore, if the simple landing page has all of those lacks, it stands to reason (since the app. is written by the same folks that created the landing page) that the app. may likely have all the same lacks, and possibly even more.