Because I am bottling from a keg (which is carbonated) to a bottle. To do this, there is less foaming if:
1) You reduce the serving pressure from the keg to as low as you can get while still getting a flow. (I actually take the keg off of gas, vent it (mostly), and then use it. When the flow stops completely I turn on the gas for a couple/few seconds, and repeat.)
2. You reduce the temperature of the bottles by freezing them.
3. You cap immediately.
I've done this for a bunch of batches and after some practice, it works great. I've had beer that I did many months ago and it is still nicely carbonated.
See this thread for details:
https://www.homebrewtalk.com/f35/we-no-need-no-stinking-beer-gun-24678/
Advantages:
1. Let's you carbonate in the keg. No sediment in the bottles. No guessing at proper carbonation level (you can adjust it once carbonated in the keg).
2. Let's you take your beer with you, while still normally enjoying your stuff on tap.
3. Free's up keezer space. Once the keg starts getting "light", I will typically bottle the rest. I do this because my keezer is full and I have another keg (or more) waiting to be put in the keezer.
Dis-advantages:
1. Harder to do than initial bottling, as the beer is already carbonated. Takes a bit of practice, you might get a couple/few "beer sprays" on you at first.
2. Requires kegs etc.