"Over the weekend, due to rough sea conditions, SpaceX's recovery team was unable to secure the center core booster for its return trip to Port Canaveral," SpaceX representatives said in an emailed statement. "As conditions worsened with 8- to 10-foot swells, the booster began to shift and ultimately was unable to remain upright. While we had hoped to bring the booster back intact, the safety of our team always takes precedence. We do not expect future missions to be impacted."This is the time of year when it's very common for the area around the Cape to get strong winds off the ocean and those winds bring rough seas. While it's a shame to see them lose the booster, reality is the system has to be designed for these seas. Balanced all the while against the cost of a ship that much bigger and more stable than the ones they're using.
It's widely reported that the ships are autonomous, and the crews are relocated onto another ship that stands back well away from the drone ship while the landing attempt is made. The first step is for a crew to return to the ship and secure the booster to the deck by welding hold down brackets to the landing feet on the Falcon 9, according to the Wikipedia entry. The statement from SpaceX makes it sound as if they viewed it too dangerous to deploy the welders onto the drone - or to leave them there if they were already aboard.
When you look at the feet of the booster, remember these things are a lot bigger than you might think.
The same view with some workers near the legs adds perspective. Those hold downs aren't standard U-bolts you're going to find at Ace Hardware.
And the Atlantic off the Florida east coast gains another stretch of artificial reef a bit over 225 feet long and 12 feet across.