If salvation is possible from all religions, then is proselytizing required? There are some Christian groups who believe that all religions are inherently good
and that a good person who rejects Jesus Christ will still go to Heaven. According to them, if good people can go to Heaven regardless of what their religion is, then do we still have to tell them about Jesus Christ or we can just leave them alone to worship their own god, gods or goddesses?
Short answer
Because Jesus is that important to you, and you want him known to all the world.

Swedenborgianism
From the linked question, I am assuming you are asking on the perspective of Swedenborgianism, which is forms the doctrinal foundation of the New Church
Evangelism
According to Dream Prophecy

New Church tends not to evangelize, and respects people's free will in thinking on their own. Nor does it condemn other religions to hell.

That said, according to NewChurch.org historically they did evangelize, in the form of spreading awareness.

In the latter part of the century, the ministry almost doubled in size and an expansion of evangelization work was initiated to spread awareness of the new teachings and further grow the church.

Salvation
According to Swedenborg.org

Salvation is an inner experience rather than acceptance of a particular doctrine.
The Second Coming is an active process that is happening within us and the world. As we increase compassion, integrity, understanding, and healing in our lives, we are helping God create a &quot;new Heaven and a new Earth.&quot;

From Arcana Coelestia 6488

A discussion about predestination once took place and many of the
spirits, owing to the chief ideas they had adopted in the world, were of
the opinion that some people have been predestined to heaven and others
to hell. But I heard a response to this from heaven, which was that no one
has ever been predestined to hell, but that all have been predestined to
eternal life

Why Evangelize?
From the above, it seems that in a Swedenborgianism perspective it is not necessary to evangelize concerning salvation.
From Swedenborg Study

The Lord Jesus Christ is our God. There is no other. To Him we owe all that is good and all that is true. All power in heaven and on earth is His. To Him alone should we pray. To Him alone should be our worship, our love, and the service of our lives.

From Heavenly Doctrines.org

To make known that the Lord is here


The agencies for this Proclamation are many,-organization, the priesthood, preaching and public worship, printing and publishing the books of the new Revelation, and other modes of evangelization, that men may know that the Lord is here.

Even if you believe that Salvation is for all, but you believe that Jesus is the only one true God, you will still want others to know Him as well.