They are careful in spending money because indeed their finances do not allow them to make them wasteful in spending, including bringing in players who will drain their pockets. One of the good and cheap options is to look at young players who have potential that can be developed, the money they will spend will not be so much and also when they succeed in building the character of the player it will become a strong foundation for their squad in the future . Especially now that young players are getting a lot of attention, and in fact most teams are focusing more on young players now.
They are careful because their finance is not too good and they aware that other clubs will improve and compete for top four more seriously. Top four competition will become more difficult and the last season is only a start but AC Milan only got a position in top four at very last matches.
That race will be harder with improvements of AS Roma and Juventus in a new season. Juventus will not have big point reduction like in the past season and they will have a fairer race with AC Milan. AS Roma with their last season in the current contract with Mourinho will aim at top four and they will not only want to play in Europa League. They must invest more into transfer market and have better results as well as more ambitious plan to convince Mourinho.
Generally lot of challenges for AC Milan in future and if they overspend money but get worse results, lower positions, non top four positions, they will be in financial troubles.