Political labels are inherently amorphous. They mean different things to different people. So
people make assumptions about the person so labeled, which may not accurately reflect their beliefs.
I don't like being labeled a "liberal" even though most people would probably categorize my
views on 8 out of 10 issues of the day "liberal." By labeling me "liberal," you make assumptions about how I feel about all 10 issues (and so you would be flat wrong about 2 of them) and also incorrectly make assumptions about the other 8, where my views are somewhat nuanced.
The term "Socialism" is much worse; it's rife with misunderstandings and pre-conceived biases against it. In response to a question about being a Socialist, Alexandra Ocasio-Cortez
("AOC"), explained: "I believe in a moral and wealthy America, no person should be too poor to live." That's not Socialism. All Americans should believe that concept. Many do, even non-Democrats.
But by labeling it with a word that many Americans associate with Communism, enemies of America, bread lines and anti-Christian, AOC is muddying a simple, clear and winning message.
Definitionally speaking, "Socialism" is an economic system where the people (government) own the means of production (all the business). That's not what AOC, Bernie Sanders or anyone else is talking about. See Difference Between Socialist and Democratic Socialist. They are especially NOT talking about the Socialism that goes with Communism, the authoritarian political system which uses Socialism as its economic system. Unfortunately, many people - people whose votes the Democrats will need to win the next presidential election - associate Socialism with the Communist systems (e.g. Soviet Union; Venezuela) which had harsh totalitarian governments and failing economies. Nobody wants that. Efforts to distinguish THAT Socialism from Bernie’s Democratic Socialism needlessly put Democrats on the defensive and muddies the message.
In addition, "Socialism" is used to ridicule government expenditures that the speaker does not like. Amazon's decision not to move to Queens, NY based on a political backlash is a perfect example. The backlash was called "Socialist". Attaching the label "Socialist" to people who oppose giving $3.4 billion to a hugely successful private company that pays no income tax shows how silly the label can be (if anything, the $3.4B subsidy is socialist). Similarly, funding green initiatives is "Socialist", but subsiding fossil fuels is not. Programs formerly popular with Republicans and now labeled Socialist. See Bring Back Eisenhower Socialism
Let's face it, several of the Democrats' proposals are Socialism-ish: Healthcare for All; Anti-Poverty
Programs; Education; Green New Deal. They are in the direction of, but nowhere near, actual Socialism. Nobody is suggesting that government own all the business. Why cloud the issue with a term many don't understand and more even more attach a negative connotation?
Democrats need two things to win: a plan and a message. We basically agree on the plan. Here’s the message: Free market capitalism has raised more people out of poverty than any other system. But we expect government to curb its excesses. When the system leaves millions of working people unable to afford basic food, medical care and housing, government must step in. Whoever can articulate this message best, gets my vote in the Democratic primary.