Why do the two small dots on "ü" sometimes exist and sometimes not?

1. ü的拼写 Spelling rules of “ü”
ü自成音节或在一个音节开头时，前边加上y，ü上面的两点省略。例如：ü→yu、üan→yuan、üe→yue、ün→un。
When “ü” forms a syllable by itself or occurs at the beginning of a syllable, it is written as “yu”, with the two dots of “ü” dropped, e.g. “ü”→yu”, “üan→yuan”, “üe→yue”, “ün→yun”.

2. j、q、x与ü的拼写 Spelling rules of “j”, “q”, “x” and “ü”
j、q、x与ü及以ü开头的韵母相拼时，ü上面的两点省略。例如：jù（句）、xué（学）。
When “j”, “q”, “x” are put before “ü” or a final beginning with “ü”, the two dots in “ü” are dropped, e.g. “jù（句）”, “xué（学）”.

bc j, q, x cant be with u. so if u see ju, qu, xu, u wont pronounce it wrongly. so we can omit the two dots. l and n can be paired with u and ü, so when we cant omit the two dots or u will pronounce it wrongly.🤔