Joomla 3 is end-of-life, and upgrading hurts
[joomla]Joomla 3 reached EOL in August 2023. Many sites still run on it because upgrading to 4 or 5 is a full re-migration: templates need replacing, extensions often too, and the database migration is manual work. Agencies usually charge it as a new build.
[invoker]Instead of a Joomla 3 → 5 migration that costs as much as a new build: rebuild straight away on a stack without major-version pain. No future Joomla 6 that needs yet another migration.