Everyone has different experiences and interests in college, but I recall Garbage Collection as an important subject decades before 2000. I studied CS in the 1970s (and 1980s) and garbage collection was already an important subject. It was a part of the ACM recommended CS curiculum as far back as 1968. Google Scholar reveals thousands of results for "garbage collection algorithm" before 1990. The subject was studied by great computer scientists (Lamport, Dijkstra, and Liskov are all Turing award winners) and the results were fun and interesting:

1989

  AW Appel: "Simple generational garbage collection and fast allocation"

1988

  JF Bartlett: "Compacting garbage collection with ambiguous roots"

  J Crammond: "A garbage collection algorithm for shared memory parallel
  processors"

1987

  AW Appel: "Garbage collection can be faster than stack allocation"

  DI Bevan: "Distributed garbage collection using reference counting"

1986

  B Liskov, R Ladin: "Highly available distributed services and fault-tolerant
  distributed garbage collection"

1985

  J Hughes: "A distributed garbage collection algorithm"

1983

  H Lieberman, C Hewitt: "A real-time garbage collector based on the lifetimes
  of objects"

1982

  RJM Hughes: "A semi‐incremental garbage collection algorithm"

1981

  J Cohen: "Garbage collection of linked data structures"

1977

  HC Baker Jr, C Hewitt: "The incremental garbage collection of processes"

1976

  Douglas W. Clark: "An efficient list-moving algorithm using constant workspace"

  PL Wadler: "Analysis of an algorithm for real time garbage collection"

  

1975

  Guy L. Steele, Jr.:"Multiprocessing compactifying garbage collection", CACM

  Edsger W. Dijkstra, Leslie Lamport, et al.: "On-the-fly garbage collection:
  an exercise in cooperation"
  

1974

  Gary Lindstrom: "Copying list structures using bounded workspace"

1973

  Edward M. Reingold: "A nonrecursive list moving algorithm"

1972

  H. D. Baecker: "Garbage collection for virtual memory computer systems"
  
  Ben Wegbreit: "A space-efficient list structure tracing algorithm"

1969

  Robert R. Fenichel, Jerome C. Yochelson.: "A LISP garbage-collector for
  virtual-memory computer systems"
  
  Joseph Weizenbaum: "Recovery of reentrant list structures in SLIP"

1967

  H. Schorr, W. M. Waite: "An efficient machine-independent procedure for
  garbage collection in various list structures"

  Peter J. Denning: "The working set model for program behavior"

1963

  Daniel J. Edwards: "Secondary Storage in LISP"

The Communications of the ACM, during this period, was the most read CS Journal. Articles appearing there were intended to be of interest to the widest population of computer scientists and 19 of them were on garbage collection.

LISP, APL, LOGO, ML, Prolog, CLU, Scheme, Cedar, Smalltalk, Icon, SML, Mathematica, J, Haskell, Python, Dylan, Self, Lua and Javascript are all important, garbage collected programming languages that came before the late 1990's.