Are we still going on about the g**damn welders?! Allow me to explain this from the non-fan, non-way-too-much-thought POV:
The ship is under construction: what is the most recognizable way to depict that? Welders. Joe Schmo, the potential consumer, will recognise what is going on with no explanation. They're welding a hull = big ship being built.
The alternative is to use some more advanced, 'realistic' depiction, such as growing the ship with crystals or using some nano-bot thing, which would require ten minutes of geeky documentary exposition for Joe Schmo to understand, at which point he'll have decided three things:
1. Not seeing that bullshit.
2. Must get another chilli-dog.
3. Fondle girlfriend.
Welders are definitly the way to go.