Star Wars Memes

One in-universe argument would be that you generally have more precision and striking force with two hands, as opposed to one-handing. This somewhat mirrors some of the "Longswords" that were designed to allow two-handed use, but could also be used with one. Using two weapons at once effectively isn't quite as easy in real life as it's made out to be in games and movies (not impossible, just harder to coordinate) but Jedi could obviously circumvent that issue by being space wizards.

Using a Blaster in the second hand would therefore sacrifice melee capabilities, where it seems their command of the force gives them a significant edge over most opponents.

Of course, the ranged capabilities might offset that, but I assume that, up to the Clone Wars, Jedi didn't often deal with a large number of ranged combatants. Where their reputation wasn't enough to deterr attacks, their premonition and weapon capable of deflecting shots will have dealt with most attackers, and if they're ambushed in close quarters the sword would be more useful too.

My reasoning here is that both protections and weapons usually evolve in response to evolutions in the other. If Jedi often enough faced fire so heavy that deflection alone wasn't enough and some kind of armor would have increased their chances of survival, I would assume they'd wear some (as you see it in the Clone Wars cartoons and the Old Republic games). Equally, if situations where a ranged weapon would have been desirable were a common occurrence, I would assume that the Jedi would eventually have adopted them.

Some degree of reluctance may be explained by religious adherence to their sacred weapon, such that they stuck with it even when the situations they faced evolved during the Clone Wars. Additionally, adopting new doctrines can take time even among less dogmatically rigid organisations.

As someone else replied, a survivor of the Jedi Purge did end up incorporating the Blaster into his arsenal. Without the Order's dogmatic constraints or a lifetime's worth of "This is what I've always been using", the barriers of acceptance are much lower. Compounding this, the new threat environment features professional, highly trained soldiers that – memes notwithstanding – are genuinely dangerous marksmen. Under the circumstances, expanding your arsenal beyond the traditional is the pragmatic choice of "uncivilised" survival over dogmatically pure death.

Or just stop your enemy's heart with your mind.

I have no source for this, but I believe there are some who can do that. It's just that focusing your force to reach deep into a living creature's body isn't quite so trivial to do in the middle of combat.

Or use your super-fast running abilities to jab a fork in your enemy's eye or something.

At that point, what's the advantage of the fork over the lightsaber? But I'd assume improvised weapons are a part of their arsenal too, it's just not as flashy as the bright lightsabers.