There is a contradiction in terms in "only" generating practical endgame tablebases. We have to understand how tablebases are generated to see why.
Tablebases are generated by working backwards from the final mating/drawing positions, "retracting" moves rather than playing them forward. First, every possible final position is exhaustively listed. Then from each, we "retract" (take back) moves that could have been played. In doing so, we know a possible outcome of the resulting position (by playing forward to the final position again). Do this for all positions, and we know the ideal outcome of all of them.
Now what is a retraction? Pieces move backwards, so everything moves as in normal chess except pawns. Pieces can uncapture other pieces, leaving an extra piece on the board. Notably, pieces can unpromote into pawns.
Herein lies the problem. If you want to evaluate the "practical" endgames, you need to know all the final positions that could lead to them by retractions. If we agree KPPP v KB is a practical endgame (seems so), then we need to know the outcome of all KQQQ v KB endgames, since it might be the case that the only winning line is to reach a winning KQQQ v KB endgame. It is necessary to do these "trivial" endgames in order to do the practical ones.
(Preemptive counter-counterargument: not all KQQQ v KB positions are winning. Think of stalemates. This is another reason why we cannot handwave and say "all positions with this material balance are winning".)
Furthermore, the absurd KQQQ v KB might be necessary to correctly generate results for KQPP v KQBP or some dramatic pawn race endgame. If you don't check all the possible final positions (even absurd ones), you can never be sure that you didn't miss the only winning/drawing line.
The only possible "optimisation" of this sort you can do is to not generate, say K+6 v K endgames (which I think was the case for the 7-men tables, they skipped K+5 v K until everything else was done.)