"Does anybody know for sure what's going on at a technical level?"
No, because I'm sure it is not exactly the same cause(s) for each and every case. From what I observe being the common reasons are an incompatible computer or the computer meets minimal system requirements but some try to play as if a computer that can handle a lot of mods/cc/EP's or the graphics card is not even being recognized for whatever reason (I wonder if some even have their computer connections in the right place...you know actually connected to the dedicated graphics card by VGA/DVI/HDMI cable and not the motherboard which may be by default to use its own integrated graphics) or mods/cc in general and being ignorant of how it affects game performance concerning poly count, being badly made/containing errors, not coordinating the same patch level for mods/cc, hidden conflicts with other mods/cc, etc or trying to play the game with settings that the computer cannot handle.
From my understanding, the most common issue concerning TS3's performance is on the user's end. There's so many different configurations of computers and ways for TS3 to function well or not. That's the whole point of the system requirements is to showcase and tell what is and is not compatible with the game. Unfortunately, TS3 didn't have any official recommended system requirements for the best experience and only provided the minimal. But is it really that difficult to figure it out? No. For one, there's enough information from people with certain graphic cards/CPU's/etc to research performance capabilities. Two, TS3 lifespan was from 2009-2013, however, I am not sure they added any more updates concerning addition of compatible hardware in 2013.
Which brings me to this observation. What if newer hardware and features/operating systems/newly released computers are not even compatible with TS3? Again, there is a reason why system requirements are used and are important to follow for the best experience for any game unless officially stated otherwise. Because computers have so many different configurations, I think that is the main reason why some have issues with TS3 because of their lack of understanding about computer hardware, how it all works and affects game performance among other things.
And yes, TS3 works fine without a gaming desktop or laptop but no one said that all EP's/SP's/Store Content/Mods could all be installed too and still run okay. Computers have a limit to what it can handle and games have a limit to what it can handle. That's the whole point of improvements, advancements in upgrades.
Is TS3 horribly programmed/coded? Actually, that can be subjective or objective depending on the actual expertise of having worked on games and done a lot of coding to know what is good vs bad and the why something is done the way it is. Sometimes it's because of a logical reason like limitations, etc. Subjectively, I think TS3 is fine as gameplay without mods/cc because performance-wise it runs at its best in my personal experience. I rarely nowadays, if ever, get error code 12 or crashing to the desktop which are the most two annoying issues I constantly have when using mods/cc. Everything loads up a lot faster without mods/cc putting an extra strain on the CPU/GPU. However, I try not to go crazy with mods so my game performance is still mostly minimal to no lag, however, with the unexpected two most annoying issues.
The game has glitches of course, but most I encounter are minor and/or have workarounds for it whether with or without mods. Most, if not all, of the major game breaking issues from patches, etc have been addressed. Or so I haven't come across anything recently.
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@CheesySimsLover
If that were true about TS3, then there's no way anyone could have a positive and good experience with the game. I'm sure there are many who can deny that claim about the open world bringing down performance. Specifically, those who don't use mods/cc and are knowledgeable about their own chosen hobby. It is true that TS3 is the most ambitious Sims game ever created, however, not at the expense of performance for the most part. If that were the case and as bad as some claim it is, I wouldn't be still playing 9+ years. And I'm the type to easily get frustrated when games don't work like they should. Not to mention, if it were so bad I highly doubt it would have continued to outsell TS2. Because word of mouth is quite effective, don't you think? So effective, that even misinformation gets spread about like truth for those who don't do their own research and just accept whatever they read and hear as truth. Or just accept their own experience as the truth that everyone has the same exact performance issues. It's the open world's fault, huh? It's all programmed/coded so poorly I can't even play and enjoy the game as is without mods and all EP's/SP's/Store Content installed and all in-game settings maxed out. :trollface:
https://youtu.be/MZfGDCoFf2U
https://youtu.be/RecjZIs6N-E
https://youtu.be/eGZxSsm5sUc
