You mean a Franco-Lithuanian Alliance? There is literally nothing Lithuania contributes to this alliance in, it'll be the recipient of a defense treaty, needing the protection of a sugar daddy. That's it. Plus, France would have to defend Lithuania against either Germany or the USSR, and if literally anything happens, France is too far away to do jack shit but give angry protests. If the USSR invades it, France would need German permission to go through its territory, and if Germany invades it, all France can do is a diversionary attack on Germany's western border. And given how absolutely tiny Lithuania's population and military is, Germany wouldn't need more than a pittance to run it over while deploying most of its army against the French. So the French gain nothing out of this.What about an Alliance with Lithuania instead?
And if you're talking a Polish-Lithuanian alliance... yeah, not happening. See, the Poles stole quite a bit of territory from Lithuania, and they don't trust them one bit in return. Also, again, Lithuania has a very small population, little industry, and can contribute nothing to an alliance on its own.