> Why there were no fundamental discoveries in physics since the quarks in 1968?
There have been; 1968 was the first physical evidence supporting quarks, but the top quark wasn't observed until 1995.
That's kind of important, because a lot of effort between 1968 and 1995 went into fleshing out the theory around the quark model and confirming it, including hunting down the theorized ones not yet observed. Heck, the six quark model wasn't even proposed until the 1970s, much less confirmed.
Now, if you want to revise the question to “since 1995”...
Then we’ll talk about the Higgs boson, theorized in 1964 (just like the original quarks) but confirmed in 2012.
There have been; 1968 was the first physical evidence supporting quarks, but the top quark wasn't observed until 1995.
That's kind of important, because a lot of effort between 1968 and 1995 went into fleshing out the theory around the quark model and confirming it, including hunting down the theorized ones not yet observed. Heck, the six quark model wasn't even proposed until the 1970s, much less confirmed.
Now, if you want to revise the question to “since 1995”...
Then we’ll talk about the Higgs boson, theorized in 1964 (just like the original quarks) but confirmed in 2012.