A fair point is that Brazilian youngsters are not as dominant at U18/U20 tournaments as they were before. Brasil won 4 editions in a row between 2001-2007 (generations 1982-1988), which fed the senior team for many years but recently, Brasil couldn't reach to even semis in last two junior WCH whereas. So it is not trainers don't give them a chance in NT, it is also the fact that there are not such exceptional players anymore to get a slot among such a competitive pool of senior players.
yes, and clubs know that. they're having a hard time hiring good OHs, for example. minas keeps hiring pri daroit, who's over 30yo and never shined in the NT, simply because that aren't any good ones that could potentially make them strong. gabi, natália and probaby drussyla (if she regains her pre-injuries form) are the only viable candidates. perhaps amanda and jaque too, but that's already a stretch.
but part of the problem is that talented and promising players are not necessarily given chances... until this past season, lorenne and borgo were bench players. and then given a chance, they shined and showed what they can do... of course, i don't think borgo will be the savior of the NT but lorenne might well be...
that's another thing. if the NT for example fails to reach F6 in the VNL because the coach let youngsters play and gain experience, criticism would come crashing down hard on everyone. there's a lot of expectations on the NTs here and hardly room to breathe. we saw what happened in 2018 and 2019 with plenty of players refusing to join simply because the pressure is way too high. it's a hard thing to work around.