I'm gonna be as blunt as possible with you. It's the fact that the message is boring. Everyone uses it. Nothing in it stands out or makes your FC seem anymore different then another.
Here's my advice, and not everyone may agree with this. Let's start by dissecting your message.
1): "Two Airships"
I see this one a lot, and I really don't understand the point of it. Unless your giving the recruit free access to your airships; I never understood why people would advertise this. Despite that, it does attract people regardless and that's the objective. If one those airships has access to Diadem hard, you should advertise that to. Even though more then half the community finds it boring as hell, just knowing that you have the option to do it is enticing for recruits.
2): "Craft Tables"
This one is kinda expected that most FCs with homes have at this point especially if you have a mansion. IMO, you could leave this out to add more characters to your message.
3): "Able helpers"
This one is also kinda expected from FCs. It's a little bit of a given cause most FCs are generally helpful if you ask.
4): "Mansion"
Keep this one. That one is important. This is one of those major things that says, "My FC has this, others do not". It stands out. That's exactly what you want.
Things you should include in my opinion are: Mention if your Airships have Diadem Hardmode unlocked. And add that your LGTB friendly. This is highly attractive to people to see even though most FCs are anyway. Also say "Casual/Hardcore/Roleplay" if your any of those. Another thing that will grab certain players attention is if your message has a hook. A jingle or funny message. Also there's nothing wrong with shouting. Some people will tell you they don't do it because they don't like it, but truth be told, it does work; and those who don't like it are usually the ones perfectly happy in their current FC. They of course arn't your target. (just remember haters are gonna hate there. Just don't spam it. Like, shout in the zone once every 10-15mins or so). Contrary to popular belief; shouting is actually a good way to make your FC known. People may not join right away, but they may consider your FC eventually. I also suggest making a PF ad to advertise as well.