there are multiple reasons for the drop in number of transactions and lack of demand is not one of them. granted the number of investors may have decreased due to the end of the big bull run but that is not lack of demand it is the fake demand going away. the real demand is still there and it is increasing day by day.
The introduction of SegWit increased the block size <stripping unnecessary baggage and fitting more tx's into a block> and this made spam attacks more expensive.
ummm, no.
everything about spam attacks are still the same. the spammers can, at any time, start the same spamming operation and with the same type of transactions (P2PKH and specially P2SH which takes up bigger space) to fill the blocks right up and increase the size of mempool.
SegWit can not do anything about that.