There always is, and they rarely do these days.
Of course there's bound to be an exception at some point. It's just that we literally haven't had one in over a decade.
Yes, but we've already seen more from Zverev, Tsitsipas, and FAA at their respective ages than we've seen from any of the "Lost Gen" guys. There's also some serious depth among the younger players. Consider the number of players <25 currently in the live top 100:
5. Zverev (22)
6. Tsitsipas (20)
9. Khachanov (23)
13. Medvedev (23)
14. Coric (22)
21. Auger-Aliassime (18)
24. Berrettini (23)
25. Shapovalov (20)
26. De Minaur (20)
27. Djere (24)
30. Edmund (24)
32. Garin (23)
35. Tiafoe (21)
38. Kyrgios (24)
41. Fritz (21)
48. Norrie (23)
52. Hurkacz (22)
55. Jarry (23)
60. Ruud (20)
61. Opelka (21)
63. Humbert (20)
66. Nishioka (23)
69. McDonald (24)
75. Sonego (24)
78. Rublev (21)
82. Kecmanovic (19)
85. Bublik (21)
86. Harris (22)
87. Munar (22)
89. Moutet (20)
101. Popyrin (19)
(I added Popyrin because he's on the fringe)
Now dial that back almost five years, to year-end 2014/beginning of 2015:
8. Raonic (24)
11. Dimitrov (23)
22. Goffin (24)
39. Thiem (21)
42. Sock (22)
43. Janowicz (24)
51. Carreno Busta (23)
52. Kyrgios (19)
53. Pospisil (24)
56. Tomic (22)
59. Struff (24)
60. Delbonis (24)
61. Schwartzman (22)
66. Vesely (21)
69. Lajovic (24)
80. Rola (24)
86. Berankis (24)
92. Kuznetsov (23)
100. Krajinovic (22)
102. Coric (18)
Kei Nishikori was #5 but turned 25 on December 29.
Obvious the first list is not only longer but younger. Now let's dial it back two years, to age 22 and younger, and create one list. Five years ago is in bold, with current live rankings in normal:
5. Zverev (22)
6. Tsitsipas (20)
14. Coric (22)
21. Auger-Aliassime (18)
25. Shapovalov (20)
26. De Minaur (20)
35. Tiafoe (21)
39. Thiem (21)
41. Fritz (21)
42. Sock (22)
52. Kyrgios (19)
52. Hurkacz (22)
56. Tomic (22)
60. Ruud (20)
61. Schwartzman (22)
61. Opelka (21)
63. Humbert (20)
66. Vesely (21)
78. Rublev (21)
82. Kecmanovic (19)
85. Bublik (21)
86. Harris (22)
87. Munar (22)
89. Moutet (20)
100. Krajinovic (22)
101. Popyrin (19)
102. Coric (18)
As you can see, the top seven players on the combined list are all of the current young generation - you have to get to 8th, Dominic Thiem, to get to one of the older guys.
This is not to say that all of this is proof that we're on the verge of some young player(s) rising to dominance, but simply that it is a much stronger crop of young players than Lost Gen was five years ago.