Because, as
@one has already explained, you're basically saying 'this is the law, but I'm not enforcing it', and whilst you may get away with it, you're opening up a very dangerous can of worms for when something happens later on in the match and players start wondering why you're not making exceptions in those situations.
Additionally, believe it or not, it will get you a reputation among the players and at some point that reputation is going to feedback into the refereeing system and it is not something you'd want hanging above you.
Do you apply the law 100% on every occasion for dissent and OFFINBUS? If not you are doing the exact same thing just without any explanation or visible interaction to deal with the player and offence.
Dissent? Yes. 100%, because early on in my career I was consistently docked points going for promotion because I didn't deal with clear dissent appropriately, taking similar lines of reasoning as you did.
Since I started cautioning dissent at every opportunity, my match control has become more secure and my marks have gone up. In my experience, observers love a referee that will caution dissent and take a dim view of referees who avoid it.
As for OFFINABUS, I think that people make the situation harder than it needs to be by trying to blur the lines between 'industrial' language and OFFINABUS, but also by trying to rationale that they have to be offended or insulted personally by such language. Context matters, obviously, but if a player is making a remark to you about your family, wife, kids, parents, whatever, they are generally trying to insulting, offensive or abusive. That you find their comments so pathetic that it doesn't even register as offensive or insulting or abusive to you personally, I feel, is besides the point, they know what they're trying to do and so, should be punished accordingly.
Also, I feel it needs to be pointed out, sometimes the best education you can give a player in regards to the LOTG is to give them a caution/dismissal for the offence they commit.
That is educational, and for all you know, these players may have been sent off many a times for these offences and you're taking a massive assumption that they're clueless about certain aspects of the law, in order to give them a weaker sanction (or no sanction), in which case, they've pulled a blinder and are laughing all the way back to the changing rooms. So, punish the offence, get yourself a reputation as a referee that will punish those offences, rather than a referee who might look naive, or as my old assessments used to say; 'wishy-washy'.