That's a fair point, and you are right to say that subjective isn't a term in the laws. But is is trotted out by officials left right and centre to justify stuff. Which often is fine. There are plenty of decisions that are genuinely subjective. To use an example, if you had 20 seasoned football fans who have all played the game at a certain level and understand it well, you often get a penalty or red card where 10 will say yes, 10 will say no. Its a genuinely tough call. If you are on the wrong side of one of those then suck it up. Its gone against you, and fans, managers and players whining in those situations are equally responsible for the bad feeling towards officials as the officials making mistakes.
But on occasions the split will be far higher, 17/18 people would say penalty, 2 would say no penalty. So technically subjective, but you wonder what the the 2 have been smoking/drinking. A good recent example of this I feel is the recent penalty Arsenal should have had v Newcastle. Gyokeres absolutely wiped out by Pope, Pope looks guilty as sin, pen all day long. but for every 10 people saying "I cant believe that they have overturned that" you were getting one saying "yeah, but he does nick the ball with his toe". The whole thing then gets buried in a file marked subjective