So if any single one of your used services leaks your password, you‘re essentially screwed since the root can be determined. Have you heard of haveibeenpwned.com?
I used to use this as well (with site-specific part in the middle, not as a suffix) but then switched to Bitwarden and random passwords as some suffixes were not unique and with 300+ services it started being annoying to type over and over again. Also a more sophisticated attacker could intercept two passwords and see the similarity, then bruteforce just the difference.
Ok, so some guy in Croatia now knows the root, so what? How does that help them? They can't access the other suffixes without physical access to my home computer. Not to mention they have no idea which part is the root and which part is the suffix