It is common for years to pass with the server left entirely to the company that built your site. Why not take stock once of whether the cost, configuration, and security still fit your situation?
Your monthly server cost has an opaque breakdown, and you cannot tell whether the amount is really reasonable.
You have left the server entirely to the company that built your site, and you do not know whether the current plan fits your site's scale.
You are on a higher-tier Xserver, CPI, or Sakura plan and suspect you are over-provisioned and paying too much.
You have never had a third party check whether your WAF, SSL, and backups actually work.
You have a maintenance contract, but when you ask, all you get back is "no issues at present," with no basis you can verify.
After the site was delivered, you have no one to consult on an ongoing basis about operation, updates, and incident response.