Except for the 1987 design mini's. However, the real question to ask is why do they do it. One reason is to get old timers on baseball cards. Topps, I think a few years ago bought the rights to use their images on baseball cards. So if you bought the rights to use Babe Ruth's image then why not put him on baseball cards. However, that still does not explain why Topps feels it has to six or seven inserts.
I think you can really trace the beginning of the insert set craze to Fleer in 1991 and 1992. They began putting inserts sets in their Football, Baseball and Basketball sets. These usally came 2-4 inserts per 36 pack box. Prior to this Donruss (Elite), Pro Set (Lombardi Trophy) and Upper Deck (Reggie Jackson autographs) had some super rare inserts (rare at the time). By 1995 Fleer started to put out 6-7 inserts sets and even had what they called were Hot Packs where all the cards in the packs were inserts.
Why does Topps have so many inserts. The first and major reason: They think or know that it makes them more profitable. They had to have done some sort or marketing or profit loss analysis to determine how they could get optimal sales out of their product. Instead of having more cards of relief pitchers and backup infielders they give us cards of Babe Ruth and Hank Aaron. That makes some sort of sense. With 25 men rosters over 30 teams, 750 major league players can be spread out over 3 - 330 card series. Most teams will get 20-25 different players in all 3 Topps series (1, 2 and update.) .
But do the insert cards have any value for the collector. No and it makes putting together complete sets by collectors that much harder. The second reason why Topps has some many inserts sets. Exclusiveness. In the middle of the decade, Topps had very few insert sets. They started increasing the number around 2008 (as maybe Topps were beginning to eye an exclusive contract with Major League Baseball).
The reason is inserts are so boring, is how could they not be, when you try to have six or seven every year, creativity goes out the window.