Making melee carries work means they need to be able to "get away with" a similar item build to ranged carries. That is, 1 defensive item max for the rest being offence.
If that were to stretch to melee carries needing 2 defensive items to survive then... maybe... but it already feels like a lot of bruisers are staying near 2 defensive items and going damage elsewhere anyway (Trinity, Cleaver, Hydra, Botrk) and getting away with it. Jax tends to not really build defensive items much at all and gets away with it...
Tryndamere works because he gets... at least 5 seconds of damage, or has to be focussed with CC for a noticeable period of 5 seconds. Plus he needs to get to low health first. This has been the "toxicity" issue with tryndamere being workable as a carry for... ever. Focussing him hurts you, not focussing him hurts you. Always a threat. Has minuscule commitment issues compared to everyone else.
Other characters are forced to use their "carry" ults almost immediately in any team fight situation and are VERY easy to bait / disengage from (Olaf [once upon a time bro], Yi, Sion, Poppy, etc)
Gangplank is probably the only other melee carry who can go melee carry and still have some degree of something going for him (his ult can be used for hard engages, W gets him out of things once he's in there, Q harass is pretty significant with damage items). He still can't ever auto attack though.
The melee carry "efficiency" item of Ghostblade was also nerfed for no reason at the same time as Cleaver. Hurting melee carries (-5 or 10 armor pen, -5% CDR, -2 seconds on the active, slightly less AD IIRC?) and keeping the cost the same. I'm surprised riot are making these mistakes at this point, but whatever. It's like "Zed is dominating the game", "better nerf Irelia" all over. Except "Cleaver op" -> "better nerf one of the most underused items in the game that no one was building in any way shape or form in the first place". Commitment issues also exist on what was once considered to be the Melee carry efficiency item of choice.
Other good/efficient items for melee carries are better on bruisers or aren't giving enough immediate effects to their build paths for melee carries to work with. Lizard Elder is great cost efficiency but isn't scaling with AS and also works with single target abilities [could make the true damage effect be a stacking one so its "better" for melee carries / less gay on ezreal / etc]. Hexdrinker is giving mediocre AD and MR (for an AD carry) but scales well with bruisers already defensive aspects better than it does on melee carries; derpo. Maw is a pretty big expensive gap and is basically the perfect Melee carry item, but it really sucks to build it/rush it, and Melee carries want the bonus AD from Maw ASAP for it to be worth building... hence it isn't worth building.
Defensive items good for carries have been nerfed because they were too good on ranged carries multiple times throughout history. No adjustments. Melee carries become usable when there are single available items that give great spikes in survivability (old warmogs). Arguably they go from warmogs rush (like the other bruisers at the time) into offensive items just as well if not better than bruisers. *ding ding ding ding ding ding ding ding*. <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
tl;dr commitment. Riot needs to make melee carries not so full of commitment, or at least give them something more for committing. Right now what they get isn't enough. Imagine for a second if ghostblades active was something like "grants % movementspeed for X seconds while approaching enemy champions, upon auto attacking for the next Y seconds gains the DPS stuff" (and has some CD reductions maybe for not AAing in time while still approaching champions). Suddenly I don't feel like I have a wasted item just because they saw/heard the active. Sword of the Divine kinda has the right idea (X seconds or Y AAs) but I think the item is 'weak' over all though (and if it was much better it would be the ADCs ****** it).
So, a single defensive item that doesn't make ranged or bruisers or ad casters OP.
Maw not being a ****ty build path.
SotD/Ghostblade not being ****. Imagine if SoTD kept it's regular attack speed after using the active but only for melees? Holy **** would the item suddenly be a really ****ing good melee carry item. That would probably need gold efficiency adjustments so it isn't good on every melee character.