Unstable Nginx with "stable" webgateway

So, we have docker image webgateway-nginx, marked as latest-em, which means supposed to be extended maintenance

$ docker run -it --entrypoint bash containers.intersystems.com/intersystems/webgateway-nginx:latest-em

root@9ca3373fe980:/# /opt/nginx/sbin/nginx -V
nginx version: nginx/1.21.5
built by gcc 11.4.0 (Ubuntu 11.4.0-1ubuntu1~22.04) 
built with OpenSSL 1.1.1n  15 Mar 2022
TLS SNI support enabled
configure arguments: --prefix=/opt/nginx --with-pcre=/opt/pcre-src --with-zlib=/opt/zlib-src --with-openssl=/opt/openssl-src --with-http_gunzip_module --with-http_ssl_module --with-http_v2_module --add-module=/opt/nginx-src/csp

root@9ca3373fe980:# /opt/webgateway/bin/CSPnsd -h    

InterSystems CSP - Network Service Daemon

   Version 2024.1.2.398.0 Gateway Build 2401.1845 (Multi-Threaded)

Gives nginx version 1.21.5, version that lost support more than 2 years ago

And to add a bit more

Versioning Scheme

The open-source NGINX project maintains two branches: mainline and stable.

• mainline: Mainline is the active development branch where the latest features and bug fixes get added. It is denoted by an odd number in the second part of the version number, for example 1.21.0.
• stable: Stable receives fixes for high‑severity bugs, but is not updated with new features. It is denoted by an even number in the second part of the version number, for example 1.22.0. The stable branch never receives new functionality during its lifecycle and typically receives just one or two updates, for critical bug fixes.

So, why EM version of webgateway got unstable version of Nginx, which is anyway outdated for more than 2 years?