Given that the median transaction sizes are so similar between Monero and Bitcoin (see this question), what other contributions are there to the overall blockchain size (e.g. database overheads or other Monero-specific contributions)?

I ask as someone not terribly familiar with databases and blockchain storage codebases between different cryptos. I don't see why there is so much concern over Monero's scalability with respect to blockchain size if the median transaction sizes are so close, unless there are other factors I am not aware of.

Edit: I have just realised that the statistics linked to in the answer to the question linked refer to the median block size, despite saying transactions size. If there are empty blocks then obviously that will bring down the median block size. What I am interested in is the median transactions size when compared to Bitcoin. If anyone can shed light on this then it would be much appreciated.