Let me tell you why.

After using 3 TSO to seal one of Madara’ limbo. Naruto is seen with having 6 left. [1]

Then he uses a TSO to make a bijudama rasenshuriken. That means there’s 5 to go before he runs out. [2]

With more meteors falling, he spawns 7 of the same attack(Presumably, the five central ones used TSOs, while the ones on the end didn’t). Leaving him with no TSOs to spare. [3]

In fact, as IT was casted and while Naruto was protected inside sasuke’ susanoo, he is shown yet again to not have any TSOs on stand by. Once susanoo is released, you can see TSOs returning to Naruto’ back. [4]

This isn’t unique to Naruto either.

Not only was Madara’ lower half able to generate not a whole new set of TSO,

Madara’ Lower Half

Manga Scans [5]

Anime Scans Pt.1[6] Pt.2[7] Pt.3[8]

his top half was used to make an ETSO.

Madara’ Top Half

Manga Scans [9]

Anime Scans Pt.1[10] Pt.2[11] Pt.3[12]

All this took place after Madara had no TSOs left as well.

Madara With NO TSOs

Manga Scans [13]

Anime Scans [14]

I think I’ve done enough to prove my point, TSOs Can Be Reproduced/Replenished.