Not sure if there's a better reasoning quoted in some source, but as per Memory Alpha:

According to various sources, when Gene Roddenberry was deciding what to call what has come to be known as Star Trek, "Wagon Train to the Stars" was one of the names he toyed with.

Obviously, wagon train does have a connotation of "slowly migrate with difficulty", so in that context the choice of "Trek" fits pretty well.

The above (sadly un-sourced) Memory Alpha info matches the info on the Wiki:

Roddenberry had extensive experience in writing for series about the Old West that had been popular television fare earlier in the 1960s and the 1950s, and he pitched his new show to the networks as "Wagon Train to the stars."

The source for the Wiki info is listed as "25th Anniversary television special"

Interestingly enough, the original title seems to have been given a new life in "Star Trek: Wagon Train to the Stars" - a novel #1 (of 6) written by Diane Carey for "Star Trek: New Earth" series.

Not sure if there's a better reasoning quoted in some source, but as per Memory Alpha:

According to various sources, when Gene Roddenberry was deciding what to call what has come to be known as Star Trek, "Wagon Train to the Stars" was one of the names he toyed with.

Obviously, wagon train does have a connotation of "slowly migrate with difficulty", so in that context the choice of "Trek" fits pretty well.

The above (sadly un-sourced) Memory Alpha info matches the info on Wikipedia:

Roddenberry had extensive experience in writing for series about the Old West that had been popular television fare earlier in the 1960s and the 1950s, and he pitched his new show to the networks as "Wagon Train to the stars."

The source for the Wikipedia info is listed as "25th Anniversary television special"

Interestingly enough, the original title seems to have been given a new life in "Star Trek: Wagon Train to the Stars" - a novel #1 (of 6) written by Diane Carey for "Star Trek: New Earth" series.

Not sure if there's a better reasoning quoted in some source, but as per Memory Alpha:

According to various sources, when Gene Roddenberry was deciding what to call what has come to be known as Star Trek, "Wagon Train to the Stars" was one of the names he toyed with.

Obviously, wagon train does have a connotation of "slowly migrate with difficulty", so in that context the choice of "Trek" fits pretty well.

The above (sadly un-sourced) Memory Alpha info jibes with The info on the Wiki:

Roddenberry had extensive experience in writing for series about the Old West that had been popular television fare earlier in the 1960s and the 1950s, and he pitched his new show to the networks as "Wagon Train to the stars."

The source for the Wiki info is listed as "25th Anniversary television special"

Not sure if there's a better reasoning quoted in some source, but as per Memory Alpha:

According to various sources, when Gene Roddenberry was deciding what to call what has come to be known as Star Trek, "Wagon Train to the Stars" was one of the names he toyed with.

Obviously, wagon train does have a connotation of "slowly migrate with difficulty", so in that context the choice of "Trek" fits pretty well.

The above (sadly un-sourced) Memory Alpha info matches the info on the Wiki:

Roddenberry had extensive experience in writing for series about the Old West that had been popular television fare earlier in the 1960s and the 1950s, and he pitched his new show to the networks as "Wagon Train to the stars."

The source for the Wiki info is listed as "25th Anniversary television special"

Interestingly enough, the original title seems to have been given a new life in "Star Trek: Wagon Train to the Stars" - a novel #1 (of 6) written by Diane Carey for "Star Trek: New Earth" series.