Legends not Showing up in R plots-CodePudding

I am working with R. I made the following plots:

#create data
a = abs(rnorm(100,10,10))
b = abs(rnorm(100,10,10))
i = 1
c = data.frame(a,b,i)
c$col = as.factor(ifelse(c$b>10,"red", "blue"))

a = abs(rnorm(100,10,10))
b = abs(rnorm(100,10,10))
i = 2
d = data.frame(a,b,i)
d$col = as.factor(ifelse(d$a>10,"red", "blue"))

a = abs(rnorm(100,10,10))
b = abs(rnorm(100,10,10))
i = 3
e = data.frame(a,b,i)
e$col = as.factor(ifelse(e$b>10,"red", "blue"))




#create data
a = abs(rnorm(100,10,10))
b = abs(rnorm(100,10,10))
i = 1
c = data.frame(a,b,i)
c$col = as.factor(ifelse(c$b>10,"red", "blue"))

plot_1 = plot(c$a, type = "h", col = c$col, main = "plot_1, i = 1")



plot_2 = plot(d$a, type = "h", col = d$col, main = "plot_2, i = 2")



plot_3 = plot(e$a, type = "h", col = e$col, main = "plot_3, i = 3")

I am trying to add legends to all of these plots:

plot_1 = plot(c$a, type = "h", col = c$col, main = "plot_1, i = 1")


legend(1, 95, legend=c("Sampled", "Not Sampled"),
       col=c("red", "black"), lty=1:2, cex=0.8)

plot_2 = plot(d$a, type = "h", col = d$col, main = "plot_2, i = 2")

legend(1, 95, legend=c("Sampled", "Not Sampled"),
       col=c("red", "black"), lty=1:2, cex=0.8)

plot_3 = plot(e$a, type = "h", col = e$col, main = "plot_3, i = 3")

legend(1, 95, legend=c("Sampled", "Not Sampled"),
       col=c("red", "black"), lty=1:2, cex=0.8)

But none of these legends are showing up. Does anyone know why these legends are not working? I know how to do this in ggplot, but it is not working with the base plots in R. I am following the instructions from this website here: