"Get Smart" is one of the funniest TV comedies of all time, but someone who didn't grow up when it was regularly airing would never know. 

We live in an age of unprecedented television accessibility thanks to the rise of streaming services. There are more new shows than ever each year (hundreds upon hundreds), but also more old shows than ever available. Where once we had to rely on syndicated or cable reruns to enjoy "The Brady Bunch" or "The Golden Girls," now anyone can pull them up on Amazon or Paramount+ or Hulu at our leisure. 

Despite the multitude of classic TV shows available on major streaming services like Netflix, Amazon, Hulu, HBO Max, Disney+, Paramount+ and Peacock, many series aren’t possible to stream at all. 

Seminal series including “Smart,” “Laverne & Shirley,” “Mork and Mindy,” “WKRP in Cincinnati” and “Homicide: Life on the Street” aren’t on any major paid or free subscription service. Some aren’t even available to purchase digitally. It’s a darn shame, not just for the older generations who grew up watching these shows and want to revisit them but for younger ones who never get to experience the drama and hilarity. Just as our cultural memory grows longer, thanks to newfound accessibility, series left out will fade further from the view of new generations who consume their art by algorithm. 

History is important, even if it’s the history of a medium so many see as frivolous and lowbrow. 

The business decisions of the major streaming services aren’t always transparent, so it’s hard to find out exactly why "The Twilight Zone," which premiered on CBS in 1959, is streaming (on Paramount+), but "Gilligan's Island," which premiered in 1964, isn't.

The bottom line is, streamers look for programming that will bring them more subscribers and revenues. If there isn’t a big enough audience for “Knots Landing” that will bring or keep more subscribers and their fees than it costs to stream it, the nighttime soap will stay off the internet.

Another factor part of the equation is music rights, a legal minefield as songs that appear in many TV shows were only licensed for the limited on-air runs, and sometimes home video. Streaming rights were never even contemplated. 

When most of us look for something to watch on streaming, the major paid services come to mind: Netflix, Hulu, HBO Max, Amazon, Hulu, Apple and even Peacock and Paramount+. But, especially when it comes to classic TV from the 1950s to '80s, a goldmine of content is available on free, ad-supported streamers like Freevee, Roku and Tubi. Cord-cutter cable alternatives like PlutoTV and Fubo also have great content. Shout Factory, an entertainment company focused on releasing cult and historical films and TV, has some series available on its small streaming service.

Here are a few classic TV shows available to stream for free, with commercials: 

And some good news for fans of TV classics: The more streaming services enter the streaming wars, the more series become available, including sitcoms “Good Times” (CBS, 1974-79) on Peacock and “The Odd Couple” (ABC, 1970-75) on Paramount+. 

40 best TV shows to watch on Paramount+: 'Twin Peaks,' 'Evil,' 'Twilight Zone'

35 best TV shows to watch on Peacock: 'Good Times,' 'Alfred Hitchcock Presents'

Streaming is easy, convenient and built into our daily lives. But I treasure my DVD box sets of TV shows that are important to me: The original “Batman” series; “Star Trek;” “Buffy the Vampire Slayer;” “Doctor Who.” 

As streaming services come and go (RIP Quibi, CNN+), it’s good to remember that we can’t rely on these business models to preserve art. Even if you buy a digital copy of a TV show or movie from iTunes or Amazon, you could lose it if the digital store loses the license to sell it. But that DVD of “Friends” you bought in 2007? That’s forever.