A lot of the 'feel for the water' comes from doing IM and stroke work ("major" your primary stroke in practice that is not freestyle). This forces age groupers to do whole sets in other strokes or IM. Not much of that for triathletes or pro-triathletes. For pro triathletes, maybe some shake out stuff or a warm up set with some IM order or broken IM stuff, but no drills for strokes I'll bet, and that's only for pro triathletes WITH a swimming background that know those stroke specific drills from their age group swimming days. Lionel sanders is not doing drills for back/breast/fly. Most only do freestyle sets and perhaps backstroke (freestyles cousin - i.e. same flutter kick) to mix it up. Mostly it's pulling and swimming freestyle. Just doing the work, blue collar swimming. No frills. The drills triathletes do are freestyle mostly, if any. They need to focus on freestyle (the main set and pull set) and then get the eff outta the pool to recover and get ready for the next one.
Also teaching your body the correct pathways (neural / muscular) as you are a developing child must play a big role. Our bodies might not be as mailable as we age.
Funny story about cyclists with crazy natural ability, getting on and crushing competition immediately. Stage race in Idaho in the 90's. Over the course of a week, a new to cycling, cat 4 rider (The lowest level at the time, before they added cat 5) was upgraded to a cat 2 over the course of one week, he was that freakishly good. Usually upgrading categories in cycling takes time, work, and points, unless you are a complete freak of nature, apparently. The fair process of upgrading is via accumulated points to prove your worth but that could be skipped if USCF officials thought an automatic upgrade was warranted based on skill. I was given an automatic upgrade from cat 4 to 3 during a stage race, but not from a 4 to a 2!! To jump two categories in a week is unheard of. This is the legend anyway. His name was Greg Randolph. He later did a stint for Lance Armstrong at Motorola and was his domestique in the 96' Olympics on the road before settling into mountain biking.
There must be many stories in cycling like this. The real horses are found really quick amongst the fluff. Lots of new cyclists think they are the shi* just because they get a bike, a kit, and start riding. They don't know where they stand though. Many cyclists have no perspective of their talent in relation to others, like swimming or running, where you are constantly training with others on a standardized track or swimming pool. You always know where you stand. Strava is changing that for cycling from the old days, keeping cyclists heads and ego's in check (or pumping them up!).
That is impossible in swimming, other than sprint 50's or perhaps 100's in HS only for less competitive states, where it's just churn and burn. Lots of HS sprinters in swimming are just wrestlers or baseball players, who can chuck on a suit and tear it up at the state meet with little or no feel for the water.