Pat Sajak finally reveals why 'Wheel of Fortune' always offers 'RSTLNE' in the bonus round: "We decided..."

Games on the "Wheel of Fortune" keep getting retained and updated to keep the audience engaged. There are games with rules that fans are familiar with now and many even come up with winning strategies. While nobody knows why it was introduced, Pat Sajak shed some light on the subject. One of them is the Bonus round where contestants get the same set of letters as a puzzle.

In this round on Wheel Of Fortune, contestants have a chance of winning a brand new car or up to $100,000 (sometimes $1 million). Unlike other rounds, in the finale, players get to choose the puzzle category, three consonants, and a vowel and are given the letters "R, S, T, L, and E" as the standard set.
However, before 1988, this wasn't the case. Back then contestants in the Bonus Round got to pick five consonants and one vowel and had 15 seconds to solve the final puzzle.
The rules were then changed and according to the show's veteran host Pat Sajak, it was done for the convienience of the players. In a YouTube clip, Sajak explained that the producers of the show realized that the letters R, S, T, L, N, and E were the most common letters to be chosen by players. Hence, they decided to give these letters for free, to encourage variety in the letter picks.
Post-1988, players got to choose only three consonants and one vowel, and they had just 10 seconds to solve the final puzzle. The change definitely made things more interesting for the viewers as it added another element to the game. According to Ben Blatt, author for the Slate, the standard letters represent approximately 45% of all letters in a standard English text. Despite this, they haven't been very helpful to the players.
Analyzing answers from 13,000 puzzles in the show's opening rounds and more than 2,000 Bonus Round puzzles, Blatt found that the letters RSTLNE accounted for only 29.6% of letters in Bonus Round puzzles compared to 44.7% in the regular game puzzles.
This means, that picking the right combination of three consonants and a vowel has become ever so crucial for the modern-day "Wheel Of Fortune" player in the bonus round. According to Blatt, there is a combination of letters that could statistically help out players in the Bonus Round, regardless of the puzzle.
Firstly, Blatt suggested that picking the "Phrase," or "Food & Drink" category offers a better chance of winning according to past data. Furthermore, picking the consonants H, G, B, and the vowel O provides the player with a greater chance of getting hints on the board.
According to his analysis, in all past rounds, this set of letters would have netted more wins for the contestants. If all bonus-round contestants in the past had guessed the letters H, G, B, and O at every opportunity, they would have revealed 22.5% of all bonus-round letters as per Blatt. This is because O is usually the fourth most popular letter in the language.