As I've said before, the original Traveller rules (circa 1981) are a little unclear and/or overly simplistic. It was, at the time of its development, made for pencil and paper gameplay and, with particular respect to space combat, also for tabletop miniatures. It clearly wasn't fully thought out at the time of its original publication, but it was a great concept that gained a lot of popularity. And for good reason, RPGs were catching on and lovers of the Sci Fi genre wanted in on the action.
Fast forward to today. After many years of revisions and licensed spinoffs, Marc Miller (the original creator of Traveller), started a kickstarter for "Traveller 5" in 2012, with the latest edition "Traveller 5 v5.10" being released in 2019. T5 is an extremely ambitious effort to refine and expand all the rules from character generation to space combat. While I applaud the effort and am impressed with the level of detail contained in T5, the core rulebook (5.09 anyway) is virtually unreadable, sometimes contradictory, and often indecipherable. Not to start grousing too much, but the apparent fetish Miller has for using letter designators for EVERYTHING gets confusing pretty fast (e.g. Starship Mission designation on p286). Also consider the melee combat equation on p. 185 where success is 2d6 < (Attack MN) - (Defned MN) + mods. If MN is the same for both the attacker and defender and there are no mods, then the attacker has to roll 2d6 < 0? Really? Just two people swinging at each other (and missing) for eternity?
(Here's a friendlier third party T5 review)
Anyway I don't want to go on too long like this because there are some aspects of T5 that I really like, even if they aren't well implemented in the official rules, particularly Nd6 vs d20. I'll probably expound on that in particular at some point, but my real purpose here is to explain the reasons for having a few special house rules. In a nutshell, that reason is to make the game more sensible and realistic without overburdening the gameplay. To achieve that, we'll be including some, likely modified, T5 rules to enhance the "depth" of the experience, and making some new rules up from scratch (which, to be honest, is kind of fun for me). Most of T5's complexity we'll just leave on the table, possibly to pick up on at a later date, or maybe never.
I get that since most of us have been playing 5e for years and years, this may all seem a little complicated, but I think its really just getting used to something new. Sure it'll be awkward and slow at first, but the differences are ultimately aimed at making the games play out and "feel" like "realistic" sci fi adventures. Rules are in essence limitations. Bad ones, or too many, stifle creativity, but good ones, in the right proportion, stimulate it by requiring you to work within their bounds to solve problems and overcome challenges.
(Thank you for listening to my TED talk.)