Because it doesnt invalidate anything. I'm also not getting angry about anything, dont know where you picked that from, maybe projecting something?
In Yahtzee the Small Straight is 1,2,3,4,5 and Large Straight is 2,3,4,5,6. Both have 5 dice in use. In this game, Small Straight is 3,4,5,6 and Large Straight just adds the 5th die to it. So to make more sense, they should rather be called Short Straight and Long Straight, instead of the now confusing Yahtzee-derived naming scheme.
Its the same thing if Full House was suddenly 1+2 instead of 2+3. It just wouldnt make sense to name it the same if it doesnt follow the same layout.
From my experience with other Yacht Dice (like Nintendo's Club House on the Switch), a Small Straight is usually 4 dice in a numerical sequence (so for example 2-3-4-5), while a Large Straight is 5 dice in a numerical sequence (so 1-2-3-4-5 or 2-3-4-5-6).
I guess it depends on the version though! The Wiki for Yahtzee has the same rule as the one from Club House, but I did see a board game forum's page for Yacht Dice saying that a S Straight is 1-2-3-4-5 and a L Straight is 2-3-4-5-6 (it doesn't seem like the most prevalent version, but it does exist).
I just checked and you're actually right! What the hell? This is a complete personal Mandela Effect moment for me. I very distinctly remember Small Straight always being five dice. Well, I guess I'm the one with egg on my face on this one.
I just tested and the game does recognize all 4 dice straights as small straight, so yeah, works as intended.
small straight in yahtzee is 4 dice in a row, large is 5 dice in a row. I do not know what version of yahtzee you played but 35 years ago, if you rolled 1,2,3,4 that's a small straight. Or 3,4,5,6. Small being the number of scorable dice. Maybe things have changed. Also the scoring for a small straight was a flat rate and a large I think was double that, not sure . going back a ways