Think about how you might create such a basis. Let's say for $\ell^1$. You start with the standard unit vectors, whose span merely gives you vectors which have only finitely many non-zero entries. What do you add next? Maybe $(\frac1n)$? Then $(2^{-n})$? You keep adding things in. Then you lose track of what is a linear span of what you have previously added.
It is similar to creating a Hamel basis of $\mathbb R$ over $\mathbb Q$. Start with $1$, $\sqrt 2$, $\sqrt 3$, $\pi$. Can we add $e$, or is that already in the linear span of the previous elements?
If you want to make it rigorous, you would want to show that there is a model of set theory in which $\ell^1$ does not have a Hamel basis. I found this, but it doesn't precisely answer this question.
https://mathoverflow.net/questions/233359/linear-space-with-hamel-basis-and-the-axiom-of-choice
This seems to answer your question rigorously: A Hamel basis for $\ell^p$?