Note that even the Japanese don't draw tiles around the kanji when they publish diagrams (e.g. tsume puzzles).
Traditionally, these were published in print media, such as newspapers and books. Since they were already printing Japanese text, it wouldn't be difficult for them to print half-Kanji piece names, whereas it would probably take extra equipment, such as specially made typefaces, to print full representations of Shogi pieces. It would probably also take up more space if they printed full representations of pieces in their varying sizes, and in print media, extra space costs more. At least, Japanese readers could easily tell which pieces belonged to each side by their orientation. For them, this would be as easy as it is for us to tell when Latin characters are upsidedown, and maybe even easier, as we have some letters that look the same upsidedown (O, I, H, X) and some that look like each other upsidedown (M and W, p and d). For westerners with less familiarity with the Japanese language, it helps to have pieces in wedge shapes. A computer interface for playing Shogi does not have the limitations of print media, it is not targeted at just a Japanese audience, and since it is used for playing the game instead of just solving puzzles, every way it can simulate the experience of playing across the board helps.
Traditionally, these were published in print media, such as newspapers and books. Since they were already printing Japanese text, it wouldn't be difficult for them to print half-Kanji piece names, whereas it would probably take extra equipment, such as specially made typefaces, to print full representations of Shogi pieces. It would probably also take up more space if they printed full representations of pieces in their varying sizes, and in print media, extra space costs more. At least, Japanese readers could easily tell which pieces belonged to each side by their orientation. For them, this would be as easy as it is for us to tell when Latin characters are upsidedown, and maybe even easier, as we have some letters that look the same upsidedown (O, I, H, X) and some that look like each other upsidedown (M and W, p and d). For westerners with less familiarity with the Japanese language, it helps to have pieces in wedge shapes. A computer interface for playing Shogi does not have the limitations of print media, it is not targeted at just a Japanese audience, and since it is used for playing the game instead of just solving puzzles, every way it can simulate the experience of playing across the board helps.